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This is to certify that the

dissertation entitled

Synthesis and Characterization of Polymer/Inorganic
Intercalation Compounds

presented by

Yu-Ju Liu

has been accepted towards fulfillment
of the requirements for

Ph D. degree in Chem stry

 

 

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SYNTHESIS AND CHARACTERIZATION OF
POLYMERIINORGANIC INTERCALATION COMPOUNDS

By

Yu—J u Liu

A DISSERTATION
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Chemistry

1994

ABSTRACT

SYNTHESIS AND CHARACTERIZATION OF
POLYMERIINORGANIC INTERCALATION COMPOUNDS

By
Yu-Ju Liu

Poly(ethylene—oxide), poly(vinylpyrrolidone), poly(propylene—oxide)
and methyl-cellulose have been intercalated in V205-nH20 xerogel by
mixing aqueous polymer solutions with aqueous V205 gels followed by
slow drying. Various phases of the polymer/V 205 materials were prepared
by changing the stoichiometric conditions. Irradiation with UV or visible
dramatically changes the electronic structure of V205 framework and results
in enhanced electrical conductivity. The conductivity decreases as the
polymer content increases. The thermopower data are consistent with a n-
type semiconductor.

The reaction of V205 xerogel with C6H5NH3I in a 1:4 molar ratio in
CH2C12 for 2 days yielded (anilinium)o,4V205-O.4H20 1. Exposure to air
resulted in an intra-lamellar polymerization to form {l/n(-C6H4NH-
)n}o,4V205.0.4I-l20 2. Magnetic susceptibility measurements showed a neff
of 1.3 BM for 1 and 0.87 BM for 2. The electrical conductivity of 2 (10'3
S/cm) is higher than that of 1 (10-5 S/cm) while the thermopower of 2 (-100
uV/K) is smaller than that of 1 (-20 uV/K).

AxV205-nH20 xerogels (A = K and Cs, 0.05 < x < 0.6) were

synthesized by reacting V205 xerogel with various amounts of K1 and C51 in

acetone under N2 for 3 days. X-ray diffraction and FT-IR indicated that the

pristine V205 framework is preserved. The magnetic behavior of the
AxVZOs-nflzo phases is best described as Curie-Weiss type coupled with
temperature independent paramagnetism (TIP). The Curie constant and EPR
peak-width of the AszOs-nHzO materials show a maximum value at x ~
0.3. Charge transport studies indicate a thermally activated semiconductor.
Optical diffuse reflectance spectra are reported.

Aniline and N-phenyl-l,4-phenylenediamine (PPDA) were
intercalated in HU02P04-4H20 (HUP), a-Ti(HOPO3)2-H20 (T iP) and (x-
Zr(HOPO3)2-H20 (ZrP) to form precursors for polymerization. Thermal
treatment at 130°C in air resulted in an inhalamellar polymerization of
aniline and PPDA to polyaniline. The formation of polyaniline was
confirmed by spectroscopy, EPR and magnetic susceptibility. X-ray
diffraction data indicated a monolayer of polyaniline in HUP and TiP, and a
bilayer of polyaniline in ZrP. All materials are insulators. The MW of the

polyaniline was estimated by gel permeation chromatography.

To My Love, Jui-Sui (Alice) and To My Parents, Chen-Hwa and Yu-Chai

ACKNOWLEDGMENT

The research in this dissertation would not have been successful
without the assistance and support of many sinCere persons. Foremost, I
would like to thank my research adviser Mercouri G. Kanatzidis for his
patience, wise guidance and support. I also thank the other members of my
committee : Professor J.L. McCracken, Professor J .A. Cowen for discussion

of magnetic susceptibility and Professor T.J. Pinnavaia for his helpful

comments as a second reader.

I would like to thank Professor C.R. Kannewurf, D.C. DeGroot and
LL. Schindler for charge transport measurements, Dr. W. Hirpo for 7Li
NMR measurements and discussion and Dr. J .-H. Liao for assistance on

ORTEP graphs. Many thanks go to all members in the Kanatzidis group for

their friendship and stimulating research ideas.

In addition, I would like to acknowledge Center for Fundamental
Materials Research, the Department of Chemistry, Michigan State

University, and National Science Foundation for financial support during my

graduate career.

Most importantly, I would like to give my deepest appreciation to my

mother, wife and brother for their encouragement and support .

TABLE OF CONTENTS

Page
LIST OF TABLES .................................................................. xii
LIST OF FIGURES .................................................................. xv
LIST OF SCHEMES .................................................................. xxiii
ABBREVIATIONS .................................................................. xxiv
CHAPTER I. Introduction ........................................................... 1
1.1. General Introduction ....................................... 2
1.2. Description of Host and Guest Materials
Used in the Work .................................................. 13
List of References .................................................. 32
CHAPTER 11. Synthesis, Structure and Reactions of
Poly(ethylene-oxide)N205 Intercalation
Compounds ........................................................... 44
Abstract ................................................................. 45
2.1. Introduction .................................................... 46
2.2. Experimental Section
2.2.1. Materials ............................................... 47
2.2.2. Measurements ...................................... 47
2.2.3. Preparation of V205 Xerogel ................ 58
2.2.4. Preparation of (PE0)xV205~nH20 ...... 58

vi

CHAPTER III.

2.2.5. Photoreaction of (PE0)xV205-nH20... 59
2.2.6. Preparation of Liy(PE0)xV205an20.. 59

2.3. Results and Discussion
2.3.1. Structure of V205 Xerogel .................... 59
2.3.2. Characterization of (PE0)xV205~nH20
Phases .......................................... 61
2.3.3. Structure of (PE0)XV205.nH20 ........... 67
2.3.4. Photoreaction of (PE0)xV205-nH20.... 76
2.3.5. Charge Transport Properties ................ 83
2.3.6. Alkali Ion Intercalation ......................... 83
2.3.7. 7Li NMR Studies .................................. 88
2.4. Conclusion ...................................................... 92
List of References ................................................. 94

Intercalation of V205 Xerogel with

Poly(vinylpyrrolidone), Poly(propylene—glycol)

and Methyl-cellulose ........................................... 99
Abstract ................................................................. 100
3.1. Introduction .................................................... 101
3.2. Experimental Section
3.2.1. Materials ............................................... 101
3.2.2. Physicochemical Methods .................... 101
3.2.3. Preparation of V205 Xerogel ................ 102
3.2.4. Preparation of (polymer)xV205.nH20
Intercalation Compounds ..................... 102
3.2.5. Photo-reaction ..................................... 102

V1]

CHAPT ER IV

3.3. Results and Discussion

3.3.1. Characterization of (polymer)/V 205

Phases .................................................. 102

3.3.2. Photo-sensitivity ..... , ............................ 112
3.3.3. Charge Transport Properties ................ 118

3.4. Conclusion ...................................................... 125
List of References ................................................. 126

Stabilization of Anilinium in Vanadium(V) Oxide

Xerogel and Its Post—Intercalative Polymerization

to Poly(aniline) in Air ................. 129
Abstract ................................................................. 130
4.1. Introduction .................................................... 131
4.2. Experimental Section ...................................... 13 1

4.3. Results and Discussion
4.3.1. Synthesis and Characterization of

(C6H5NH3)0_4V205-0.4H20 ................ l 32
4.3.2. Polymerization of

(C6H5NH3)0_4V205-0.4H20 ............... 133

4.3.3. Electron Paramagnetic Resonance
(EPR) ............. 141
4.3.4. Thermogravimetric Analysis (TGA).... 141
4.3.5. Molecular Weight Studies .................... 144
4.3.6. Charge Transport Properties ................ 144
4.4. Conclusion ...................................................... 147
List of References ................................................. 149

viii

CHAPTER V. Investigation of the Vanadium Oxide Xerogel

Bronzes: AxV205-nH20 (A = K and Cs) .............. 152
Abstract ................................................................. 153
5.1. Introduction .................................................... 154
5.2. Experimental Section ..................................... 155
5.2.1. Materials ............................................... 155
5.2.2. Measurements ...................................... 155
5.2.3. Preparation of V205 Xerogel ............... 156
5.2.4. Preparation of AxV205-nH20 ............... 156
5.3. Results and Discussion
5.3.1. Structure of V205 Xerogel .................... 158
5.3.2. Synthesis and Spectroscopy ................. 160
5.3.3. X-ray Diffraction ................................. 165
5.3.4. Magnetic Susceptibility Studies ........... 169
5.3.5. Electron Paramagnetic Resonance
(EPR) Spectroscopy ............................ 181
5.3.6. Charge Transport Measurements ......... 181
5.4. Conclusion ...................................................... 184
List of References ...................... I ........................... 1 88

CHAPTER VI. Polymerization of Aniline and N-Phenyl-1,4—
Phenylenediamine in Layered Metal Phosphates
by Ambient Oxygen .............................................. 191

Abstract ................................................................. 1 92

ix

6.1. Introduction .................................................... 193
6.2. Experimental Section

6.2.1. Materials .............................................. 194
6.2.2. Measurements.......... ........................... 195
6.2.3. Preparation of Layered Metal

Phosphates ........................................... 196

6.2.4. Preparation of
(C6H5NH3)1,0U02P04-0.4H20 and
H0.12(C6H5NHC6H4NH3)0.88U02P04 196

6.2.5. Preparation of

H0,6(C6H5NH3)1,4Ti(P04)2 ............. 197

6.2.6. Preparation of

H0.7(C6H5NH3)1.3Zr(PO4)2 and

H0.6(C6H5NHC6H4NH3)1.4Zr(P04)2 197
6.2.7. Preparation of

(PANI)0,94U02P04-0.5H20 (PUP),

(PANDo,8Ti(P04)2 (PT iP) and

(PANI)2,4Zr(P04)2 (PZrP) from AUP,

A2ZrP and ATiP .................................. 198

6.2.8. Extraction of Polyaniline from PUP.... 198

6.2.9. Extraction of Polyaniline from PTiP... 198

6.2.10. Extraction of Polyaniline from PZrP. 198

6.2.11. Preparation of Base Form of PANI... 199

6.3. Results and Discussion .................................. 199
6.3.1. Characterization and Polymerization of
Aniline- and PPDA-Intercalated

Compounds .................................. 1 99
x

6.3.2. UV/V is Spectroscopy ........................... 209
6.3.3. X~ray Diffraction .................................. 209
6.3.4. Magnetic Properties ............................. 212
6.3.5. Thermogravimetric Analysis Studies... 216
6.3.6. Scanning Electron Microscopy (SEM) 220
6.3.7. Gel Permeation Chromatography

(GPC) Analysis ................................... 220

6.3.8. Charge Transport Properties ................ 227

6.4. Conclusion ..................................................... 230
List of References ................................................. 231

xi

LIST OF TABLES

Page

1.]. Calculated and Measured Densities of V205-1.08DMSO

and (PE0)1,0V205-O.7H20 ................................................... 19
2.1. X-ray Diffraction Data and IF (I )l2 for V205-nH20 xerogel. 51
2.2. X—ray Diffraction Data and |F(l)|2 for (PE0)0,5V205-nH20 52
2.3, X-ray Diffraction Data and |F(l)|2 for (PE0)1,0V205°nH20 53
2.4. X-ray Diffraction Data and |15‘(l)|2 for (PE0)1,5V205onH20 54
2.5. z Parameters of V and 0 for the PEO/V 205 Compounds ...... 55
2.6. Observed and Calculated Structure Factors for

(PE0)1,0V205°nH20 ............................................................. 56
2.7. Observed and Calculated Structure Factors for

(PE0)1_5V205~nH20 ............................................................. 57
2.8. Calculated and Measured Densities for (DMSO)1,03V205

and (PE0)1,0V205-0.7H20 ................................................... 62
2.9. Summary of Interlayer Distance, Net Expansion and

Coherence Length for (PE0)xV205.-nH20 .......................... 64
2.10. X-ray Diffraction and Magnetic Data of Irradiated

(PE0)xV205-nH20 Compounds ........................................... 77

2.11. Room Temperature Electrical Conductivity and

Thermoelectric Power of Unirradiated and Irradiated

(PE0)xV205onH20 Materials .............................................. 84
2.12. Composition, Net Expansion and Coherence Length of
My(PE0)xV205.~nH20 .......................................................... 87

xii

3.1.
3.2.

4.1.

4.2.

4.3.
5.1.

5.2.

5.3.

5.4.

5.5.

5.6.

6.1.

6.2.

6.3.

Magnetic Data of Irradiated (polymer)xV2O5.nH2O ............. 1 17
Electrical Conductivity and Thermoelectric Power of
(Polymer)xV205-nH20 materials .......................................... 124
IR Vibration Energies of (PANI)0.4V2O5-0.4H2O 2,
(PANl)xV205-nH2O 3, Bulk PAN] and Extracted PAN] ...... 137
X('[‘[p) and treff Values for (C6H5NH3)0.4V205-0.4H2O and

{ 1/n(-C6H4NH—)n}0_4V205-0.4H2O ...................................... 139
Molecular Weights of Bulk and Extracted Poly(aniline). 144
X-ray Diffraction Data, F(obsd) and F(calcd) of

Cso,27V2O5-nH2O .................................................................. 157
Summary of Composition, Color, Interlayer Spacing and
Infrared Data for KxV205-nH2O ........................................... 161
Summary of Composition, Color, Interlayer Spacing and
Infrared Data for CsxV205-nH2O .......................................... 162
Magnetic Susceptibility Data for KXV205-nH2O

Compounds ............................................................................ 173
Magnetic Susceptibility Data for CsxV2O5'nH2O

Compounds ............................................................................ 174

Corrected Temperature-Independent Paramagnetism and
Calculated and Observed AE for MxV205-nH20 .................. 177
Summary of Compositions and Interlayer Spacings of

Amine lntercalated Metal Phosphates ................................... 201
IR Vibration Energies of Extracted Polyaniline from Metal
Phosphates .............................................................................. 206
Pauli Susceptibility and Curie Spin Density of PANI/Metal
Phosphate Intercalates ........................................................... 218

xiii

6.4. Molecular Weights of Extracted PAN I from Layered Metal
Phosphates ............................................................................. 229

xiv

1.1.

1.2.

1.3.
1.4.

1.5.
1.6.

1.7.
1.8.

1.9.
2.1.

2.2.

2.3.

LIST OF FIGURES

Page

Schematic representation of V205 fibril organization and
approximate dimensions (proposed by Livage et al.) ............ 15
Two views of the structure of a V205 layer in orthorhombic
vanadium oxide .............................................. 16

The structure of V205 xerogel (proposed by Oka et at.) ....... 17
Two views of the structure of a V205 sheet @roposed by

Oka et al.) .............................................................................. 18
The structure of uranyl phosphate (HUO2P04-4H20) .......... 20
The crystal structure of a-Zr(HP04)2~H20. View

perpendicular to the b-axis ..................................................... 22
Projection of a layer of a-Zr(l~IP04)2-H2O in the ab plane... 23
Different phases of polyaniline .............................................. 26
Known conformation of poly(ethylene-oxide)....... ............... 28

Schematic illustration of the proposed structure of V205

xerogel projected onto the ac plane : (a) from Livage et 01.,

(b) from Oka et al .................................................................. 60
X-ray powder diffraction patterns of films of (a) V205

xerogel, (b) (PEO)0,5V205-nH2O and (c)

(PE0)1,5V205-nH20 ............................................................. 63
Scanning Electron Micrographs of (a) V205 xerogel (b)
(PEO)0,5V2O5-nH2O ............................................................. 65

XV

2.4.

2.5.

2.6.

2.7.

2.8.

2.9.

2.10.

Transmission mode (X-ray beam perpendicular to the

layers) X-ray diffraction patterns for (a) V205 xerogel, (b)
(PEO)0.5V205-nH2O and (c) (PEO)1_5V205-nH2O .............. 68
One-dimensional Patterson functions along the interlayer c—
axis of (a) V205 xerogel, (b) (PE0)0_5V205-nH20 and (3)
(PEO)1_5V205-nH2O ............................................................. 69
One-dimensional Patterson functions along the interlayer c-
axis of (a) V205 xerogel, (b) (PE0)0,5V205-nH2O and (3)
(PE0)1,5V2O5-nH2O ............................................................. 71
Schemes of a helical (a) and planar—zigzag (b) PEO
conformation in V205 framework and their expected

electron density projections along the layer stacking

direction. (View along the polymer chain) ............................ 72
Schemes of two arrangements of planar-zigzag PEO chains

in V205 framework and their expected electron density
projections along the layer stacking direction : (a)the plane
containing the polymer chain perpendicular to the V205

sheet and (b) the plane parallel to the V205 sheet and the

PEO bilayer structure arranged in a zigzag-like fashion.

(View along the polymer chain) ............................................ 74
Projection of the electron density of (PE0)1,0V205-nH20
calculated from Oka's model and illustrations of the

deduced arrange of PEO in the interlayer space .................... 75
Magnetic susceptibility of fresh and irradiated
(PE0)0,5V205-nH2O as a function of temperature ............... 78

xvi

2.11.

2.12

2.13.

2.14.

2.15.

3.1.
3.2.

3.3.
3.4.

3.5.

3.6.

Inverse magnetic susceptibility of irradiated

(PEO)0,5V205-nH2O as a function of temperature : (i)

me), (ii) X(Curie—Weiss) and (iii) X(measured).

(X(measured) = X(Curie—Weiss) + X(T1p)) ......................... 80
Room temperature EPR spectra of irradiated (a)
(PEO)0_5V2O5-nH2O and (b) (PEO)1,5V2O5-nH2O .............. 81
Optical absorption spectra of un-irradiated (a) and irradiated
(b) (PEO)0,5V205.nH20 ........................................................ 82

(a) Four-probe variable temperature electrical conductivity

data of films of irradiated (i) (PE0)0,5V205-nH2O and (ii)
(PE0)1,5V205-nH20, and (b) Thermoelectric power data of
films of irradiated (i) (PEO)0.5V205-nH2O and (ii)
(PEO)1,0V2O5-nH2O ............................................................. 85
Width at half height versus temperature of 7Li N MR signals

for samples, (A) Li0.18(PEO)0.5V205°nH20, (B)
Li0.2V205°nH20, (C) Li0.04(PE0)1.0V205'nH20. (D)

Li0.17(PEO) 1_5V205°nH2O .................................................... 89
X—ray diffraction pattern of (PVP)1,0V205.nH20 film ......... 104
Variation of the interlayer distance as a function of x for
(PVP)XV205.nH20 ................................................................ 105
X-ray diffraction pattern of (PPG)0,5V2O5.nH20 film ......... 106
Variation of the interlayer distance as a function of x for
(PPG)xV205.nH20 ................................................................ 108
X-ray diffraction pattern of

(methyl cellulose)0,05V205.nH20 film ................................. 109

Variation of the interlayer distance as a function of x for

(methyl cellulose)xV205.nH2O ............................................. 1 10
xvii

3.7.

3.8.
3.9.

3.10.

3.11.

3.12.

3.13.

3.14.

4.1.

4.2.

Transmission-mode X-ray diffraction patterns of films of
(a)(methyl cellulose)o_05V2O5.nH20 (b)

(PVP)1,0V2O5.nH2O and (c) V205. xerogel ......................... 111
Absorption spectrum of (PVP)1,0V205.nH20 film ............... 113
Electron paramagnetic resonance of irradiated samples
(irradiation time : 12 h) .......................................................... l 15
Variable temperature magnetic susceptibility of

(PVP)1 _0V205.nH2O .............................................................. l 1 6
Absorption spectra of (PVP)1.0V205.nH20 (diffuse

reflectance mode) : (a) unirradiated film, (b) irradiation film

(12 h). The arrows at 1920 and 1440 nm indicate absorption
from water .............................................................................. 119
Four-probe variable temperature electrical conductivity for

films of : (a) unirradiated (methyl-cellulose)o_35V205.nH20

(b) irradiated (methyl-cellulose)o,35V205.nH2O ................... 121
Variable temperature thermoelectric power data for films of

: (a)un-irradiated (methyl-cellulose)o.35V205.nH2O and (b)
irradiated (methyl-cellulose)().35V205.nH2O ........................ 122
Four-probe variable temperature d.c. electrical conductivity

data for films of (a) (methyl-cellulose)o,35V205.nH20 and

(b) (methyl-cellulose)0,05V205.nH20 ................................... 123
X-ray diffraction patterns from (A)

(Cal-I5NH3)0,4V205-0.4H2O and

(B) {1/n(-C6H4NH-)n}o,4V205-0.4H20 ................................ 134
Infrared spectra (KBr pellet) of (A)

(C6H5NH3)0_4V2O5-0.4H2O and

(B) {1/n(-C6H4NH-)n}o,4V205-0.4H20 ................................ 135

xviii

4.3.

4.4.

4.5.

4.6.

4.7.

4.8.

5.1.

5.2.

5.3.

5.4.

5.5.

Variable temperature magnetic susceptibility of
(C6H5NH3)0.4V205-0.4H 20 and

{ 1/n(-C6H4NH-)n}0,4V2O5-0.4H 2O .....................................
Room temperature EPR spectra of (a)
(C6H5NH3)0.4V2O5-0.4H2O and (b) {1/n(-C6H4NH-
)n}0,4V2O5-0.4H2O ................................................................
TGA diagrams of (a) (C6H5NH3)0_4V205-0.4H20 and (b)
{1/n(-C6H4NH-)n}0,4V205-0.4H20. (Samples were dried
under vacuum prior to use) ....................................................
GPC diagrams of (a) bulk polyaniline and (b) extracted
polyaniline from {1/n(-C6H4NH-)n}0,4V205-O.4H20 ..........
Four-probe pressed pellet variable temperature electrical
conductivity data of (C6H5NH3)0,4V2O5-0.4H20 and
{ l/n(-C6H4NH-)n }0.4V205-0.4H2O ......................................
Variable-temperature thermoelectric power data of
(C6H5NH3)0,4V205-0.4H20 and

{ 1/n(-C6H4NH-)n}o_4V205-0.4H 20 ......................................
Schematic illustration of the proposed structure of V205
xerogel projected onto the ac plane proposed by (a) Livage
et 01.9 and (b) Oka et al. .........................................................
Infrared spectrum of K0,33V205-0.5H20 (KBr pellet) ..........
Spectral shifts of V=O vibration energy as a function of x :
(a) KxV205-nH2O and (b) CsxV205-nH2O ...........................
Optical absorption spectra of (a) V205 xerogel and
Cso,27V205-0.5H2O ...............................................................
X—ray diffraction patterns of (a) V205 xerogel and (b)
Cso,27V205«0.5H2O ...............................................................

xix

140

142

143

145

146

1. 48

159

163

164

166

167

5.6.

5.7.

5.8.

5.9.

5.10.

5.11.

5.12.
5.13.

5.14.

5.15.

Projection of the electron density of C3027V2O5-nH20
calculated from Oka's model and illustrations of the
deduced arrange of Cs in the interlayer space .......................

Inverse magnetic susceptibility as a function of temperature
for (a)K0,08V2O5-nH2O, (b)K(),26V2O5-nH2O and
K0,33V205-nH2O ...................................................................

Inverse magnetic susceptibility as a function of temperature
for K0.26V205-nH20 : (a) me), (b) X(Curie—Weiss) and (C)
Xm ...........................................................................................
Simplified d orbital diagrams of V4+ in octahedral, square
pyramidal and distorted square pyramidal geometry. The
latter geometry is most representative of the V4+
environment in the reduced V205 xerogel. ( AB is the
energy separation between dxz and dyz orbitals) ...................

Diffuse reflectance IR spectra of (a) KxV205~nH2O and (b)
KxV205nH2O ...............

Plot of Curie constant, C, vs x (alkali content) for (a)
KxV205-nH2O and (b) CsxV205-nH2O ................................

Room temperature EPR spectrum of K0,33V205-nH2O ........
Changes of EPR peak width as a function of alkali ion
loading for (a) KxV205-nH20 and (b) CsxV205-nH20 .........
Four-probe pressed-pellet variable temperature electrical
conductivity data of (a) Ko,39V205-nH20 and (b)
Ko,ogV205-nH2O ...................................................................

Variable temperature thermoelectric power data of
KxV205-nH20 : x = 0.39 (a), 0.33 (b) and 0.26 (c) ...............

XX

168

170

171

176

179

180
182

183

185

186

6.1.

6.2.

6.3

6.4.

6.5.

6.6.

6.7.

6.8.

6.9.

6.10.

6.11.

6.12

6.13.

Powder X-ray diffraction patterns of (a) (x-
ZKHOPO3)2'H20, (b) H0.7(CrsHsl\1H?>)1.3IZF(PO4)2 and (C)
Ho,6(C6H5NHC6H4NH3)1,4Zr(PO4)2 ...................................... 200
FT—IR spectra of (C6H5NH3)1,0U02PO4.0.4H20 (AUP)

under thermal treatment for (a) 0 week, (b) one week, and

(c) three weeks ....................................................................... 203
FT—IR of extracted PANI from (a) PUP, (b) PZrP and (c)
PTiP, and (d) bulk PANI ........................................................ 205
Thermogravimetric analysis diagrams of (a) PZrP and (b)
PTiP under air (_) and nitrogen flow (---..) ........................ 207
Differential scanning calorimetry of A2ZrP under 02 ( ----- )
and N2 (_). .......................................................................... 208
Electronic absorption spectra of (a) PUP, (b) PZrP, and (c)
bulk PANI .............................................................................. 210

Evolution of powder X-ray diffraction patterns of
(C5H5NH3)1_0U02P04,0.4H20 (AUP) under thermal
treatment for (a) 0 week, (b) one week, (c) two weeks, and
((1) three weeks ....................................................................... 211
Electron paramagnetic resonance spectrum of ATiP after
one week (---) and three weeks (_) of thermal treatment... 215

Variable temperature magnetic susceptibility data of (a)

AUP, (b) AUP/PUP, and (c) PUP. 217
Thermogravimetric analysis diagrams under oxygen for (a)
PTiP, (b) PZrP, and (c) PUP. 219

SEM micrographs of (a) HUP, (b) a-ZrP and (c) (x-TiP ....... 222
SEM micrographs of (a) AUP, (b) A2ZrP and (c) ATiP ....... 224

SEM micrographs of (a) PUP, and (b) PZrP, and (c) PT iP... 226
xxi

6.14 GPC chromatographs of extracted PANI from (a) PUP, (b)
PT iP and (c) PZrP .................................................................. 228

xxii

1.1.
1.2.
1.3.
1.4.
1.5.
1.6.

1.7.

4.1.

6.1.

6.2.

LIST OF SCHEMES

Page
Three types of host structures ................................................ 3
1.4-addition polymerization in layered CdCl4 ...................... 5

The in-situ polymerization/intercalation of pyrrole in FeOCl 6
Intralamellar thermal conversion of PPV precursor to PPV.. 8
Intrazeolite polymerization of acrylonitrile ........................... 9

A conceptive picture of polymerization in the presence of

clay ....................................................................................... 10
Intercalation of polyaniline in the silicate galleries .............. 11
Polymerization of anilinim in V205 xerogel by oxygen ....... 138

Intralamellar polymerization of PPDA to polyaniline in
zirconium phosphate ................................................ . .............. 213
Intralamellar polymerization of anilinium to polyaniline in

titanium phosphate ................................................................. 214

xxiii

ABBREVIATIONS

TGA : Thermogravmetric Analysis.

DSC : Differential Scanning Calorimetry.
GPC : Gel Permeation Chromatography.
SEM : Scanning Electron Microscopy
EPR : Electron Paramagnetic Resonance.
PEO : Poly(ethylene-oxide).

PPG : Poly(propylene-oxide).

PVP : Poly(vinylpyrrolidone),

PANI : Poly(aniline).

PPDA : N-phenyl—l ,4-phenylenediamine

xxiv

CHAPTER I

INTRODUCTION

1.1. General Introduction.

The first report of an intercalation compound was inadvertently
described by Schafhautl more than 150 years ago when he reported his
observations on attempting to dissolve graphite in sulfuric acid.1 However,
the development of the chemistry started from 1926 when Fredenhagen et al.
described the uptake of potassium vapor into graphite.2 Intercalation is a
term to describe the reversible insertion of guest species into host matrix
without changing structural integrity of the host. Literally, it refers to the act
of inserting into a calendar some extra interval of time. However, the term is
used loosely even for irreversible reactions. Generally, the host matrices
include materials with three-dimensional frameworks, two-dimensional
frameworks and one-dimensional chains, as summarized in Scheme 1.1.
They can be organic, inorganic or organometallic compounds with
insulating, semiconducting and metallic properties. Guest species can be
intercalated into hosts via ion-exchange3, acid-base chemistry4, coordination
chemistry5 and redox reactions.6

For a long time, interests in intercalation chemistry (host-guest
chemistry) were primarily focused on the properties of host materials.7-10
The role of guest species was merely to insert into host matrices and modify
the properties of these hosts. The guest species were usually metal ions and
small molecules. The intercalation of macromolecules was comparatively
few and most studies concentrated on clay materials due to the important
applications in agriculture and industry.11 For instance, polymers such as
poly(vinyl alcohol), hydrolyzed polyacrylonitrile and polysaccharides are
used as "soil conditioners" because they can improve the stability of soil

aggregates.12 The use of finely divided clays as a "filler" incorporated into

3

1. Three-dimensional framework hosts

Structure is composed of a 3-D matrix which contains

 

 

 

 

 

 

 

 

 

 

 

 

isolated or inter-connected channels. Intercalation is
,- severely restricted to guest species whose dimensions
1:: f are smaller than that of the channels.
QQ '2 Examples: Zeolites, Pyrochlores, Proteins.

 

 

2. Two-dimensional framework hosts

The structure of hosts are composed of 2-D layer units.
/ They have a high structural flrxibility with respect to
L the uptake or exchange of guest species by expansion

 

 

of interlayer spacing.

 

 

 

 

Examples:
Clays
Hydrous oxides (M(HPO4)2nH20, M : Zr, Ti, Sn),
Alkali oxometallates (ATiMOS, A = K, Cs; M 2 Ta, Nb)
Transition metal dichaleogenides (MQZ, Q: S, Se, Te),
Teansition metal oxides [ M003, AXM02(M = Fe, Co),

MOCl (M: Fe,Y)]

Graphites

3. One-dimensional chain hosts

m Host matrices are composed of 1-D chains separated by
W van der Waals gaps or eounterions. They possess a high

structural flexibility with respect to the uptake or
exchange of guest species with different size and
geometry. However, they also have poor structural
, stability toward intercalation. Compounds belonging to
VVVV the category are comparatively few.
Examples:
Transition metal trichalcogenides MQ3 ( M : Ti, Zr, Hf)
LIM0389/3

 

 

 

 

 

 

 

Scheme 1.1. Three types of host stuctures.

4

polymer matrices such as poly(vinyl chloride) (PVC) and polyethylene to
improve physico-mechanical properties has also been widely studied and
applied in industry. 13 The paper industry is one of the largest users of clays,
especially kaolinites which serve as both filling and coating agents to
improve the brightness, color, opacity and printability of the sheet. The
incorporation of naturally occurring polymers such as proteins, enzymes,
and viruses into clays has been investigated as well.14 The studies
essentially involve the use of clays for separation and stabilization of these
natural species, and the modification of their activities.

In recent decades, the remarkable electrical, optical, mechanical
properties of conjugated polymers together with the wide range of their
potential technological applications have received considerable research
attention.15 Among the many known polymers, polyacetylene, polyaniline
(PANI), polypyrrole, polythiophene, poly(phenylenevinylene) and
poly(phenylenesulfide) have been studied the most. Generally, the research
objects involve the fundamental understanding of charge transport and its
relationship with lattice structure, improvement of processibility and pursuit
of high conductivity. The conductivity of the polymers is primarily limited
by their slow carrier mobility (10‘4-10'5 cmz/V-sec.) which results from low
crystallinity and structural defects.16 With the goal of aligning polymer
chains and thus achieving higher carrier mobility, several methods have been
designed such as physically stretching polymer films,17 and chemically
preparing polymers in liquid crystal solvents and nricroporous membranes. 18
One particular way is to form these polymers within the crystalline and
confined environment of an inorganic inclusion host. Thus, control of
conformation, linearity, cross-linking, alignment, and interchain electronic

processes is possible, if the so-called topotactic principle is obeyed. In

5

addition to these, the direct structural characterization of polymers by
crystallographic methods may also be possible.

In the early 19705, Mortland and Pinnavaia first observed the
formation of conjugated polymers within confined host lattices. When the
Cu2+ exchanged clay was exposed to benzene vapor, poly(p-phenylene) was
formed in the galleries of clays.19 A decade later, Soma et al. reported the
polymerization of the benzene and thiophene in Cu2+- and Fe3+- exchanged
montmorillonites.20 A variety of spectroscopic techniques suggested the
formation of doped conducting polymers. However, these studies mainly
focus on spectroscopic properties rather than on structural and electrical
properties. The study of topochemical reactions started from Day and Tieke

in 1982—321 They have polymerized aminodienes and -diynes in layered
CdCl4 by UV and y-ray irradiation, see Scheme 1.2.

 

 

 

 

 

 

 

 

 

 

CdCI4Z' CdCl42‘
W W W W
R — R — W R R
. . —’ M
H22: H29 H29: Hzc.
NH; NH; NH3+ NH»,+
CdCl42' C9042-

 

 

 

 

 

 

Scheme 1.2. 1.4-addition polymerization in layered CdCl4 (ref 21).

However, the development of the intercalation of conducting polymers
started from the late 19803. Kanatzidis and coworkers in 1987 reported the

in-situ oxidative polymerization and intercalation of pyrrole in lamellar

6

FeOCl (the Fe3+ center acts as an oxidant to accept electrons released from
pyrrole).22 The resulting polypyrrole/FeOCl (Scheme 1.3.) showed room
temperature electrical conductivity of 1 S/cm. This remarkable reaction
opened a new way to encapsulate conducting polymers inside the interlayer
space of inorganic host lattices from their corresponding monomers. In the
following several years, our group has extended this field of research to
other conducting polymers such as polyaniline, polythiophene and
polyfuran, and other host materialsZ3 such as V205 xerogel. The properties

of these materials are intriguing, as described later.

H

N
FeOCl g /; H
FeOCl : @@n

H
FeOCl

 

FeOCl

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

d:7.98A d: 13.21 A
Scheme 1.3. The in-situ polymerization/intercalation of pyrrole in
FeOCl (ref 22).

The same method has also been used by other groups in different host
materials. The in-situ polymerization of pyrrole in channels of 3-D
[(Me3Sn)3Fem(CN)]x was accomplished by Fisher and coworkers in
1989.24 The room temperature conductivity for the polypyrrole intercalated
compound is only 7x10"5 S/cm which is much lower than that of doped

polypyrrole, but ' much higher than that of
[Li0.3(Me3Sn)3Fe“0.3FeI110.7(CN)lx.

7

Matsubayashi et al. recently reported the in situ oxidative
polymerization of anilinium, 3-methylpyrrole and 3,4—dimethylpyrrole in
VOPO4-2H2O.25 In these reactions, the V5+ centers act as an oxidizing
agent to oxidatively polymerize these monomers. The net expansion is 8.7
A and 9.7 A for poly(3-methylpyrrole) and poly(3,4—dimethylpyrrole)
intercalates respectively, consistent with pyrrole planes approximately
perpendicular to the layers.

The electrochemical polymerization of intercalated aniline in
montmorillonite was first observed by Inoue and coworkers.26 Clay-
modified electrodes intercalated with aniline were electrolyzed
gavanostatically at 20 ”Acm-2 in 2 M HCl. As the reaction proceeded, the
electrode gradually turned blue, consistent with the formation of polyaniline.
However, no spectroscopic data were described. The polymerization
process is very slow and incomplete. The product, PANI/montmorillonite,
showed a net interlayer expansion of only 3.4 A, suggesting that the phenyl
rings of PANI are parallel to the silicate sheets. This materials remains
essentially uncharacterized.

Insertion of poly(phenylene vinylene) (PPV) in M003 has been
obtained by Nazar and coworkers by ion exchange of LixMoO3 with the
precursor of PPV, poly(p—xylylene—a—dimethylsulfoxonium) chloride,
followed by heat treatment to elinrinate dimethylsulfide to form PPV
(Scheme 1.4.).27 The 5.6 A interlayer expansion observed is consistent with
a monolayer of PPV in the galleries with the aromatic ring plane nearly
perpendicular to the oxide sheets. The material shows room-temperature

conductivity of 0.5 S/cm which is one order of magnitude higher than that of
alkali doped M003.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

M003 M003
270°C
(0 era-CH) . 0 am.
SQ) n n
/ \
CH3 CH3 A M003
M003

 

 

 

Scheme 1.4. Intralamellar thermal conversion of PPV precursor to PPV

(ref 27).

The first report of formation of conjugated polymers in 3-D structures
such as zeolites instead of 2—D layered hosts was made by Chao et al. who
observed the polymerization of pyrrole in Fe3+ and Cu2+ exchanged zeolite
Y.28 The resulting materials were insulating which was explained by
insufficient amount of polymer in the zeolite to dominate the electrical
properties of the materials.

Bein and coworkers have also worked on the zeolite systems. In
1989, they reported the polymerization of intercalated anilinium in zeolite
channels by addition of an external oxidant, (N H4)2S203. 29a Using zeolites
containing Cu2+ and Fe3+ ions, they have also accomplished the in-situ
polymerization of pyrrole and thiophene inside the 3-D framework.?-9b-d
However, these materials are insulating since the conducting polymer is
embedded in an insulating three—dimensional host and cannot be accessed
electrically. Recently, they reported the encapsulation of non-charged
polymers as well. Acrylonitrile adsorbed in zeolite was polymerized with
radical initiators. Pyrolysis of the intrazeolite poly(acrylonitrile) led to the

formation of a ladder polymer shown in Scheme 1.5.30

 

Scheme 1.5. Intrazeolite polymerization of acrylonitrile (ref 30).

Similar experiments on zeolite systems were also made by the
researchers at Du Pont.31 They have used the pentasil zeolites such as 28M-
5 and Na—fi as supporting matrices in which short-chain oligomers of
polythiophene were inserted, oxidatively d0ped to the conducting state, and
finally spectroscopically characterized. They have successfully observed the
evolution of the electronic structure of doped polythiophene from monomer,
to oligomer, to polymer.

The intercalation of polymers also provides access to the preparation
of novel polymer-ceramic nanocomposites in which the host layers are well
dispersed in polymer matrices. These nanocomposites can exhibit excellent
physical and mechaniarl properties which are superior to those of individual
components. Okada and coworkers reported that e-caprolactam was
thermally polymerized in the interlayer spacing of montmorillonite yielding
a nylon-6/clay hybrid (Scheme 1.6.).3221 X-ray and TEM measurements
revealed that the silicate layers were well dispersed in the nylon-6 matrix at
an average distance of 214 A. Compared to nylon-6 , the composite showed
excellent physical properties. For example, tensile strength increased from
69 MPa for nylon-6 to 107 MPa for the composite.

10

a layer of clay

 

 

o
00 \

00 o

o o b
o O
9) 000° polymerization:
o o 0 o o
o 00080?) o o Sféfll
\ / o o 1\

polymer
Scheme 1.6. A conceptive picture of polymerization in the presence of

clay (ref 32a).

They have also investigated rubber/montmorillonite and
polyimide/montmorillonite hybrids.32t’,c The latter composite reveals
excellent gas barrier and low thermal expansion properties.

The Pinnavaia group at Michigan State University has studied the
polyether/clay system.33a Epoxy resin monomers were intercalated into
smectite clays followed by the thermal polymerization to polyether at 120-
200°C. The average distance between clay plates was about 200 A. They
have also achieved the polyimide/clay system which shows similar
properties with one reported by Okada.33b

A research group at Cornell University used Cu2+ exchanged mica-
type layered silicates as host materials for intercalative polymerization of
aniline (Scheme 1.7.).34 The resulting PANI-hybrid was insulating but
became conducting when appropriately doped. Four-probe electrical
conductivity measurements showed a value of 0.05 S/cm. This
nanocomposite is not the same type as those found on dispersion of single

layers in a continuous polymer matrix. However, the PANI-hybrid still

11

showed modified fracture toughness, storage modulus with respect to
individual components. They also found that the hybrid was more oriented
than the pristine host, probably due to the reorganization of the silicate

layers to maximize the interactions between the polymer and the host.

H3 Silicate
Silicate
H H
Caz. ., (Q
01“

Silicate

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Silicate

 

 

 

Scheme 1.7. Intercalation of polyaniline in the silicate galleries (ref 34).

Recently, they pressed a mixture of organically modified silicates and
polymers into a pellet, and heated the pellet at an appropriate temperature
producing a intercalated polymer/silicate hybrid. For polystyrene-hybrid,
the gallery height increase of 7 A corresponded to a monolayer of nearly
planar polymer chains.34C

During the past several years, our group has investigated in detail the
intercalative redox polymerization of organic molecules (e.g. aniline,
pyrrole, 2,2'-bithiophene and terfuran) in layered FeOCl and V205
xerogel.17 The resulting materials are composed of alternating conducting
polymers and semiconducting oxide layers, and possess intriguing electrical
properties arising from the combination of the two electrically active but
chemically diverse components. For instance, the charge carriers can switch
from electrons to holes, and the conductivity can increase from
semiconducting-like to metallic by varying the polymer loading. Recently,

we extended our interests to insulating polymers such as poly(ethylene-

12

oxide) (PEO), poly(vinylpyrrolidone) (PVP), poly(propylene glycol) (PPG),
and methyl cellulose. We have found that the V205 xerogel is an excellent
host not only for oxidative polymer intercalation but also for the direct
intercalation of water-soluble insulating polymers.35 The resulting
nanocomposites show interesting physical and chemical properties (chapter
2 &3).

Although the inclusion of conjugated polymers in V205 xerogel has
been well studied in the aspect of synthesis and property, the reaction
mechanism and the interactions between the polymers and the framework
are not clear yet. To approach the first issue, we intercalated anilinium into
the V205 and observed its slow conversion to polyaniline upon oxidation
(chapter 4).36 To approach the second issue, it is important to understand
the nature and properties of the reduced V205 framework alone. For this
objective, we prepared a series of reduced V205 xerogels, MXV205 (M = K,
Cs), and studied their optical, magnetic and electrical properties as a
function of x (chapter 5) .37

The known host materials which have sufficient oxidizing power to
initiate the intercalative polymerization are only a few. In order to expand
this field to other ordered host materials which have limited redox
properties, we must find the proper conditions under which intercalated
monomers can be polymerized, not necessarily by the host, but by external
power . We are interested in building up general methodologies to produce
conjugated polymers in layered or spatially confined environments. We
have found that ambient oxygen can successfully polymerize aniline to
polyaniline in layered uranyl phosphate, cr-zirconium phosphate and or-

titanium phosphate (chapter 6).38

13

1.2. Description of Host and Guest Materials Used in the Work
1.2.1 Host Materials

3) Layered Vanadium Pentoxide Xerogel (V205.1.8H20)

Porous V205-nH2O gels have been known for more than a century.39
They can be easily prepared by pouring molten V205 into water40 or by
hydrolysis and condensation of VOCl3,41 VO(OR)3,42 or metavanadic
acid43 via a 301- gel process.

The structure of V205 xerogel has been widely investigated for the
past decade by X-ray diffraction,44 electron microscopy,45 neutron
diffraction,46 etc. X-ray diffraction indicates that the V205 xerogel is a
layered material with an interlayer spacing of 11.5 A. Electron microscopy
shows that the gels are composed of long ribbon-like particles with typical
planar dimensions of 1000 x 10 nm. Recently, cryogenic electron
microscopy further suggests that small threads (100 x 2 nm) are formed first
inthe early stages of sol-gel process.45 They grow lengthwise and assemble
with others edge by edge to form ribbon-like particles. X-ray absorption
near-edge structure (XANES) spectra reveal that the vanadium atom is in a
approximately square-pyramidal geometry as in crystalline V205.47
Extended X-ray absorption fine structure (EXAFS) data“8 in the layer
stacking direction show a strong oscillation corresponding to V=O bonds
with bond length of 1.58 A, indicating that the V20 bonds point out the
layers. Two weak oscillations associated with vanadium and oxygen are
also observed at 2.7 and 3.7 A. The first one is assigned to the distance
between vanadium and water, suggesting that the vanadium center is weakly

bonded by water. The second oscillation is attributed to the distance

14

between vanadium and oxygen of the nearest V20 group in the adjacent
pyramid. The EXAFS data performed on the other two directions also show
that V-O distance is from 1.78 to 2.02 A and V-V distances are 3.1 and 3.3
A which correspond to edge sharing and comer sharing of [V05] units,
respectively. These data suggest that the square—pyramidal [V05] units
share their edges and comers with other units to form a 2-D ribbon. One-
dimensional Patterson function calculated from x-ray data in the layer axis
show a strong maximum at 2.8 A. Livage contributes the maximum to a
non-planar V-V linkage from adjacent V205 units that leads to a corrugated
ribbon model as shown in Figure 1144,49 The intra—ribbon structure is
closely related to orthorhombic V205 (Figure 1.2). The interlayer regions
are filled with water molecules which form hydrogen bonds with other water
molecules or coordinate to vanadium centers. Recently, Oka proposed that
the ribbons consist of two V205 slabs facing each other with a separation of
2.8 A close to MszOs24 (M : Na, K) as shown in Figure 1.3.50 The single
V205 sheet is composed of edge and comer sharing of [V05] units with the
vanadyl groups on the same side of the sheet (Figure 1.4.). Although most
work refers to Livage's model448, 51-2, the density measurements strongly
prefer Oka's model, see Table 1.1.

V205 xerogel is an acidic and highly oxidizing host material. The
protons between the layers can be exchanged with cations or neutralized
with bases.51 The vanadium (V5+) atoms of the framework can be reduced
by reducants52 such as iodide. It shows n-type semiconductor behavior
arising from electrons hopping between V4"'/V5+ centers.53 The room

temperature conductivity is around 10'5 S/cm.

15

 

 

 

 

 

 

"’27?"
v. ,
lLSSA 1000A
\ J
Y
lOO-ZOOA

Figure 1.1. Schematic representation of V205 fibril organization and
approximate dimensions. (proposed by Livage et al.)

l6

 

*3"

.43).“. '

c- , E:.: :.= ..I
5.8:. 3. or...

 

U

 

Figure 1.2. Two views of the structure of a V205 layer in orthorhombic
vanadium oxide. Open circles: oxygen. Solid circles: vanadium.

17

 

11.5.3.

 

 

 

Figure 1.3. The structure of V205 xerogel (proposed by Oka et al.). Open
circles: oxygen. Solid circles: vanadium.

18

f

C C

Figure 1.4. Two views of the structure of a V 205 sheet (proposed

by Oka et al.). Solid circles: vanadium. Open circles: oxygen.

19

Table 1.1. Calculated and Measured Densities of V205-1.08DMSO and
(PEO)1_0V205-0.7H2O

 

 

 

Density (g/ cm3)
Calculated from Calculated from Measured
Compound Livage's model Oka's model value
V205-1.08DMSOa 1.18 2.35 2.25
(PEO)1.0V205-0.7H20b ~1.1 ~22 ~23

 

aReported by Oka and co—workers. bMaterial synthesized in this thesis.

b) Layered Hydrogen Uranyl Phosphate (HUP)

Hydrogen uranyl phosphate HUOzPO4-4H20 is a bright yellow
layered material with an interlayer distance of 8.69 A.54 The crystal adopts
a tetragonal structure (P4/ncc) with cell parameters of a = 6.995A and c :
17.491A. The layers consist of dumbbell-shaped uranyl ions (U022+) with
the uranium center further coordinated by four equatorial oxygen atoms of
four PO43- tetrahedra. The PO43- tetrahedron and uranyl ions link into two-
dimensional sheets as shown in Figure 1.5. The galleries consist of two
water hydrogen bonded layers, roughly one-fourth of which are protonated.
The H+ atoms in the galleries can be exchanged with cations including
mono-, di and tri-valent species or neutralized with bases such as amines.36

HUP exhibits high proton conductivity, which has led to its use in
miniature fuel cells and electrochronric displays.55 The ac conductivity
reaches 0.4 S/m at 290 K measured parallel to the layers.55b The activation
energy is 31:3 kJ/mole. HUP also exhibits rich electronic absorption and

20

 

 

 

 

 

. :Uranium

$ : Phosphorous

Figure 1.5. The structure of uranyl phosphate (HU02P044H20).

21

emission spectra. The yellow solid emits intense yellow-green
photolurrrinescence with UV or near UV excitation. Spectral features
indicate that the electronic transition are dominated by the UO2+ moiety.56
The photoluminescence properties depend on guest excited-state properties

and on host—guest interactions. For example, the intercalation of n-

C8H17NH2 totally quenches the emission.56'cl
c) (Jr-Zirconium Phosphate [Zr(HOPO3)2-H20]

Amorphous zirconium phosphate has been known for a long time.57
Its good ion-exchange properties and high resistance toward temperature and
radiation attracted considerable attention. In 1964, its crystalline phase was
prepared and structurally characterized by Clearfield and co—workers.58 (x-
zirconium phosphate (or-ZrP) is a white crystalline powder prepared either
by adding concentrated H3PO4 to ZrOClz solution in presence of HF or
refluxing its gels in concentrated phosphoric acid. It is a layered material
with an interlayer spacing of 7.6 A (Figure 1.6.). The crystal is monoclinic
with a 2 906(2), b = 5.297(1), c : 15.414(3) and B : 101.71(2)°. The layers
consist of zirconium atoms lying slightly above and below the mean plane
and coordinated by phosphate groups located alternatively above and below
the plane as shown in Figure 1.7. Three oxygen atoms of each phosphates
are bound to three different zirconium atoms and the fourth oxygen bears a
proton and points into the interlayer space. Thus each zirconium atom is
octahedrally coordinated by six oxygen atoms. The interlayer regions are
composed of a monolayer of water molecules, forming hydrogen bonds with

the phosphate groups.

22

 

Figure 1.6. The crystal structure of a-ZrflIPOQz-HZO. View
perpendicular to the b-axis.

 

 

Figure 1.7. Projection of a layer of a-zirconium phosphate in the ab plane.

Solid circles : Zr. Open circles : O. Shaped circles : P.

24

or-Zirconium phosphate exhibits a rich and varied intercalation
chemistry.59 This arises from the high acidity and weak forces between
layers. Organic molecules (such as amines, alcohols, glycols) and metal ions

have been intercalated into a-ZrP via ion—exchange and acid-base reactions.
(1) a-Titanium Phosphate [Ti(HOPO3)2-H20]

(Jr-Titanium phosphate is a member of group(VI) phosphates.
Crystalline a-TiP can be synthesized by refluxing its gel in concentrated
H3PO460. The gel is prepared by slowly adding TiCl4 into H3P04 solution,
(Jr-Titanium phosphate (a-TiP) has the same structure as (Jr—zirconium
phosphate. It is a layered compound with an interlayer distance of 7.6 A.
The interlayer space is filled with a layer of water molecules. The ion-
exchange capacity is 7.76 meq/g, slightly higher than 6.64 meq/g of or-
zirconium phosphate.61 The application on ion—exchange and catalyst have
been widely investigated.59,61'2

1.2.2. Polymer Guest Species

a) Polyaniline (PANI)

Polyaniline, probably the oldest synthetic organic polymer, has been
know for over a century.63 It is currently of great interest because of the
ability to control its electronic and optical properties through changes in
protonation and oxidation.64 Polyaniline consists of head-to—tail coupling of
aniline molecules and can be prepared as a film by electrochemical oxidation
or as a powder by chemical methods.65 Depending on the oxidation states,

PANI has three forms, named "leucoemeraldine", "emeraldine", and

25

"pernigraniline".66 The leucoemeraldine form is composed of reduced

H H
. @H . .
repeat umts, EC 11, the emeraldrne form consrsts of

alternative reduced oxidized repeat

units, @N—Q—N—Qégn and the pernigraniline from

is composed of oxidized repeat units, +0 -9 N+11. The
relationships between these forms are shown in Figure 1.8. Among them,
emeraldine is the most interesting best studied. It is insulating (1010 S/cm)
at its neutral state but becomes highly conductive (200 S/cm) after
protonation. The structural, electrical, optical and magnetic properties of the
emeraldine form have been extensively studied by several types of
spectroscopy67, X—ray diffraction68, nuclear magnetic resonance (NMR)69
and electrical conductivity.70 Optical spectroscopy of the emeraldine base
(unprotonated) shows a Jt—to-Jt* gap of 3.8 eV and an exciton absorption of
~2 eV, while the emeraldine salt (protonated) has no 2 eV absorption, but
instead exhibits two new absorptions at 1.4 and 2.9 eV, assigned to polaron
bands.67 The emeraldine base (prepared by extracting bulk emeraldine base
with THF and NMP) is proposed to be isostructural to poly(p-phenylene
sulfide) and poly(p-phenylene oxide).68 Charge transport studies show the
metallic nature of the islands formed, and the conduction occurs via
charging-energy-limited tunneling between the islands.70 The molecular
weight (MW) of PANI depends on the preparation conditions.71 The PANI
prepared chemically has average MW between 66,000—78,000. However, by
lowering the aniline concentration and polymerization temperature, the MW
(Mw) in excess of 400,000 has been obtained. Thermogravimetric analysis

has shown that the emeraldine base is much more stable than the protonated

26

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27

form.72 The base form decomposes at 450°C while the protonated form
(when anion is chloride) decomposes at IUD-250°C due to the loss of HCl.
The application of these interesting optical and electrical properties to
batteries,73 acid/base indicators,74 corrosion inhibitors,75 electrochromic
materials76 and microelectronic devices77 has received a great deal of
attention. The first commercial product, a 3-V coin-sized primary battery,
appeared in 1987. It was manufactured by a joint venture Bridgestone and
Seiko in Japan. An anti-corrosive coating to protect steel against salt is

expected to be commercialized in the near f uture.78

b) Poly(ethylene-oxide) (PEO)
‘i‘ CHTCHZ‘O ‘i'n—

Poly(ethylene-oxide), the simplest structure of water-soluble
polymers, is a semicrystalline material with ~70% of the bulk being
crystalline and the remaining present as an amorphous phase.70 Pristine
PEO adopts a helical conformation with seven monomer units and a thread
of 19.3 A per unit as shown in Figure 1.9. Under stretching or pressure, a
planar zigzag conformation of PEO is observed in which the repeat unit
contains two monomers with a period of 7.12 A71 The polymer is quite
stable chemically. In air, peroxide formation and UV chain cleavage are
responsible for a slow molecular weight decrease over months. The melting
point of the crystalline phase is Tm ~ 65°C and the glass transition
temperature is Tg ~ -60°C.

PEO has received a lot of attention because of its ability to complex

various salts giving solid polymer electrolytes (SPE).72 The maximum

28

% __.__

mo helix ”30 Zigzag

 

123A

712A

 

2

Figure 1.9. Know conformation of poly(ethylene-oxide).
Open circles : 0. Solid circles: CH2.

29

stoichiometry of the complexes depends on the size of cations and anions.
For example, the small cations (Li+ and Na+) give a 3(monomer unit) : 1
(cation) adduct while potassium and ammonium salts tend to keep the 4:1
ratio. In addition, large anions such as C104 and A5136" form a 6:1 complex.
Systematic studies of ionic conductivity versus composition and temperature
for various salts have been extensively reported.72 The amorphous
elastomeric phases in PEO electrolytes are responsible for the ionic
conductivity. Usually, the conductivity is in the range of 103-10"4 S/cm at
100°C, and falls to 10'6-10-8 S/cm at room temperature.

The application of PEO-based electrolytes on solid—state batteries and
electrochromic devices has motivated most of the research in the field.72
Technologically, SPE makes it possible to manufacture all-solid state cells
without the difficulties generally associated with the use of liquid
electrolytes such as safety and environmental stability. In addition, thin
films can be easily achieved with SPE. This results in a more reversible

electrochemical process and a higher overall energy efficiency.

c) Poly(propylene-oxide) (PPO) / poly(propylene-glycol) (PPG)

-<CH2-<|:*H-0).-
CH3

PPO has the same backbone structure as PEO.79.82 while PPO has
true asymmetric carbon atoms. Crystalline PPO is isotactic and the
molecular chains have a slightly distorted planar zigzag conformation.
Atactic PPO is completely amorphous and is known to dissolve alkali metal

salts to form amorphous polymer electrolytes. PPO shows much weaker

30

solvating property than PEG, and thus electrolytes capable of complex
formation are limited to lithium and sodium salts. This is thought to be due
to the fact that negative effect of the steric hindrance exerted by the methyl
groups which predominates over the increased donor power of the oxygen
atoms. Ionic conductivity of the FPO-alkali metal salt complexes is

comparable with that of the PEO complexes in the range of 10‘5 S/cm.

d) Poly(vinylpyrrolidone) (PVP)

fer”)

a
n
:O

PVP is a polar polymer with a Tg of 453K.79.82 It is an important
commercial polymer with a large number of uses. It is readily soluble in
water and many organic solvents, and is compatible with many plasticizers,
inorganic salts and other resins. Bulk PVP is fully amorphous and
hygroscopic but highly stable. The most important applications of PVP are
in pharmaceuticals and cosmetics. It is also capable of dissolving lithium

salts but this produces poorly conducting films.72

e) Methyl cellulose

 

OMe

31

Methyl cellulose is a derivative of cellulose and water-soluble.79.82
Cellulose is the most abundant of all naturally occurring organic compounds
found in wood, seed, leaf etc. Chemically, it is a polysaccharide, consisting
with glucose anhydride units linked together through the 1 and 4 carbon
atoms with a B-glucosidal linkage. Crystalline cellulose adopts a straight
chain conformation.82 The two anhydroglucose units are nearly co-planar
with the -CH20H side chains in successive units occurring on opposite sides
of the chain. Large amounts of cellulose and its derivatives are used in
films, plastics, protective coatings, adhesives and in many other important

industrial products.

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J.M.; McCall, R.P.; Epstein, A.J. Synth. Met. 1991, 41-_43_, 735-738.
((1) Hsu, C.-H.; Peacock, P.M.; Flippen, R.B.; Manohar, S.K.;
MacDiarmid, A.G. Synth. Met. 1993, Q, 233-237.

(72) (a) Kulkarni, V.G.; Campbell, L.D.; Mathew, W.R. Synth. Met. 1989,
32, 321-325. (b) Hagiwara, T.; Yamaura, M.; Iwata, K. Synth. Met.
1988, 25, 243-252. (c) Yue, J.; Epstein, A.J.; Zhong, Z.; Gallangher,
P.K.; MacDiarmid, A.G. Synth. Met. 1991, 42—4_3, 765-768.

(73) Kitani, A.; Kaga, M.; Sasak, K. J. Electrochem. Soc. 1988, 2491-2496.
(74) Syed, A.A.; Dinesan, M.K. Synth. Met. 1990, 36, 209-215.
(75) (a) Mengoli, G.; Musiani, M.M.; Pelli, B.;Vecchi, E. J. Appl. Polym.

Sci. 1983, E, 1125-1136. (b) Noufi, R.; Nozik, A.J.; White, J.;
Warren, L.F. J. Electrochem. Soc. 1982, 129110), 2261-2265.

43

(76) Akhtar, A.; Weakliem, H.A.; Paiste, R.M.; Gaughan, K. Synth. Met.
1988, E, 203—208.

(77) (a) Paul, E.W.; Ricco, A.J.; Wrighton, M.S. J. Phys. Chem. 1985, &,
1441-1447. (b) Chao, S.; Wrighton M.S. J. Am. Chem. Soc. 1987, @,
6627-6631.

(78) Schoch, K.F.; Saunders, H. IEEE Spectrum , 1992, 52—55.

(79) Molyneux, P. in Water-Soluble Synthetic Polymers ; CRC press, Inc.:
New York, 1983 Vols. 1, 2.

(80) (a) Takahashi, Y.; Sumita, 1.; Tadokoro, H. J. Polym. Sci. Polym. Phys.
Ed. 1973, 11, 2113-2122. (b) Takahashi, Y.; Sumita, I.; Tadokoro, H.
J. Polym. Sci. Polym. Phys. Ed. 1981, 19, 1153-1155.

 

 

(81) "Polymer Electrolyte Reviews " McCallum, J.R., Vincent, C.A., Eds.;
Elsevier Applied Science: London, 1987 and 1989 Vols. 1, 2.

(82) Ott, E.; Spurlin, M. in High Polymers; lnterscience Publishers, Inc.,
New York, 1954 Vol. 5.

CHAPTER II
SYNTHESIS, STRUCTURE AND REACTIONS OF

POLY(ETHYLENE—OXIDE)IV2 05 INTERCALATION
COMPOUNDS

44

45

ABSTRACT

Intercalation and structural characterization of poly(ethylene-oxide)
(PEO) in layered V205 xerogel, its physicochemical properties and lithium
ion redox intercalation are reported. The synthesis of PEON205
composites is achieved by simply mixing aqueous solutions of PEO with
aqueous V205 gels. After slow water evaporation, a PEON205 intercalate
is formed. Various phases of PEO/VzOs composites are obtained by just
changing the stoichiometric conditions. The interlayer distance of
Peo,vzos.nnzo varies from 13.2 is, at x = 0.5 to 16.8 A at x = 1.0, to
17.6 A at 1< x < 3, and to 18.3 A at x .>_ 3. However, bulk PEO phase is
found when x > 2.0. One-dimensional electron density calculations based
on X-ray diffraction data (perpendicular to layers) show that the
composites contain a monolayer of PEO molecules when x < 1 and bilayers
when x _>_ 1. The conformation of PEO chains between the layers is a
planar zigzag. These intercalation compounds are water swellable and light
sensitive. The photo-induced reaction dramatically changes the electronic
structure of V205 which results in enhanced electrical conductivity and
decreased solubility. The conductivity decreases as the PEO content
increases. The thermopower data and increased magnetic susceptibility of
the irradiated products are consistent with the increased V4+ concentration
and a n-type semiconductor. By reaction with lithium iodide, the
PEO/V205 composites can be intercalated with lithium. Variable
temperature 7Li solid state NMR studies of the Li/PEON205 materials are
reported.

46

2.1. Introduction

In recent years, the synthesis of polymer/inorganic nanocomposites
has received considerable attention1'3. These materials, in principle, can
possess electrical, optical and mechanical properties which may not be
achieved with each component separately. V205 xerogel is a very reactive
layered host material.4 It can be intercalated by either cation-exchange,
acid-base chemistry and redox reactions. In the past several years, we have
reported that monomers (i.e. aniline, pyrrole and bithiophene) can be
oxidatively polymerized and intercalated into the intralamellar space of the
host.5 Recently, we successfully used the swelling properties of the gels in
water to open a way to directly intercalate water-soluble polymers6 such as
poly(ethylene—oxide) (PEO).

PEO has the simplest structure of water-soluble polymers. Its
complexes with salts can be solid electrolytes and have attracted
considerable research attention because they are promising for applications
in solid state batteries and electrochromic devices.7 Systematic studies of
ionic conductivity versus composition and temperature for various salts
have been extensively investigated. However, the studies of the PEO
complex inside a constrained environment such as the galleries of 2-D
inorganic hosts were comparatively rare.8‘11 Ruiz-Hitzky et al. reported
that phyllosilicates containing Li+ and Na+ ions can act as host materials
for PEO intercalation.8 The resulting materials show higher ionic
conductivities than those for the parent alkali-exchanged silicates. The
similar method was also applied to layered transition metal chalcogenides,
MPS3 (M = Mn, Cd).9 Recently, encapsulation of PEO into MoSz was
accomplished by taking advantage of the exfoliation property of this

47

dichalcogenide.10all This intercalation compound showed very high
electrical conductivity (0.1 S/cm) due to structural distortion of MoSz.
Preliminary results for (PEO)0,5V205-nH20 phases have been
reported earlier.63 The composite material showed interesting photo-
sensitivity and could accept Li+ ions in the framework by the redox
reaction with Lil. Further investigation led to the synthesis of several
PEO/V205 phases with varying polymer loading. Here, we report the
synthesis, structural characterization and systematic investigation of the
chemical and physical properties as a function of PEO loading. We also
report the synthesis of Li+ intercalated phases and the studies of their

properties by 7Li N MR spectroscopy.
2.2. Experimental Section

2.2.1. Materials
Poly(ethylene-oxide), with molecular weight (MW) of 1x105 and
5x106, Li] and NaV03 were purchased from Aldrich Chemical Co.,

Milwaukee, WI and were used without further purification.

2.2.2. Measurements

Infrared spectra were collected from 4000 to 400 cm'1 with a
resolution of 4 cm'1 on a Nicolet 740 FT-IR spectrometer. Samples were
recorded in pressed KBr matrixes or as free standing films under N2 flow.

X-ray diffraction was carried out on a Rigaku rotating anode X-ray
powder diffractometer, Rigaku-Denki/RW400F2 (Rotaflex), at 45KV and
IOOmA with a scintillation counter detector and a graphite monochromator

to yield Cu Ka (wavelength 1.54184 A) radiation. Data were collected at

48

room temperature over the range 2° S 20 S 100° in increments of 001°.
Samples were directly coated on X-ray sample slides for reflection mode
measurements. For transmission mode measurements, composite films
were taped on a sample slide with a hole in the center. The sample slide
was perpendicular to the X-ray beam and the detector collected data from
2° to 60° in 20 with a speed of 1°/min. The coherence length was

determined from the half width of peaks using the Scherrer formula12 :
1..th = KA/BCOSO

L is the coherence length along the Miller indices (hkl), A is the wavelength
of the X-rays used, K is Scherrer's constant and has a value of 0.9, 0 is the
Bragg angle, and B is the peak width at half-height in radians.

Thermogravimetric analysis (TGA) was performed on a Shimadzu
TGA-50. Typically 5-10 mg of sample was heated in a quartz crucible in
air from room temperature to 1000°C at the rate of 5°C/min.

Electron Paramagnetic Resonance (EPR) spectroscopy was obtained
using a Varian E—4 spectrometer operating at 9.5 GHz (X band) and at
room temperature. Solid samples were scanned from 2700 to 3700 gauss
at 8 gauss field modulation and 0.03 second time constant. The g value was
obtained with reference to the standard diphenylpycrilhydrazine (DPPH).

Magnetic susceptibility measurements were done on a MPMS
Quantum Design SQUID system (Superconducting Quantum Interference
Device) with a magnetic field of 5000 gauss. A known quantity of sample
was placed in a plastic bag and purged with Ar gas. Data were collected
with an ascending ramp from 5K to 300K and then corrected for the
diamagnetic components which were obtained from the literature.13

Scanning Electron Microscopy (SEM) was done with JEOL-JSM 35

CF microscope at an accelerating voltage of 20 KV. Samples were glued to

49

the microscopic sample holder with conducting graphite paint.

Direct-current electrical conductivity and thermopower
measurements were performed in the usual four-probe geometry with 60
mm and 25 mm gold wires used for the current and voltage electrodes
respectively.14 Thermoelectric power measurements were made by using
a slow ac technique with 60 mm gold wires serving to support and conduct
heat to the sample, as well as to measure the voltage across the sample
resulting from the applied temperature gradient.15

Optical diffuse reflectance spectra were measured at room
temperature with a Shimadzu UV-3101PC double beam, double
monochromator spectrophotometer. Samples were placed above BaSO4 on
a sample holder. BaSO4 powder was used as a reference. The absorption
spectrum was calculated from the reflectance data using the Kubelka-Munk
function: a/S=(1-R)2/2R. R is the reflectance, a is the absorption
coefficient and S is the scattering coefficient which is practically
wavelength independent when the particle size is larger than 5 um.16

7Li NMR spectra were recorded on a Varian 400 MHz instrument
using a wide line Varian probe equipped with a variable temperature (VT)
control, at a frequency of 155.45 MHz. All samples were run with a
repetition delay time of 1 sec with typical 90° pulse of 2.8 us.

One—dimensional Patterson function and electron density (ED)
calculations were based on the X-ray reflection data. Six 001 reflections
were used for the V205 xerogel out to docs = 1.43 A, ten reflections were
used for (PEO)0,5V2OsonH20 out to doom = 1.35, twelve reflections were
used for (PEO)1,0V205-nH20 out to doom = 1.34 and eleven reflections
were used for (PEO)1,5V205-nH20 out to (10012 = 1.42 A. The intensities

were obtained from the integrated peak areas. The structure factors, F, of

50

these reflections were derived from their intensities and corrected by

Lorentz-polarization effects, see eq (2.1)

|F(l)| = (I/LP)1/2 ’ (2.1)
where I is the peak intensity and Lp is Lorentz-polarization effects.

Lp = (1 +cos220)/(sin20cos0) (2.2)

The IF (1)]2 values for V205 xerogel, PEOo,5V205-nH20,
PEO1,0V205-nH20 and PE01_5V205-nH20 are shown in Tables 2.1, 2.2,
2.3 and 2.4, respectively. The 1-D Patterson functions were calculated

according to eq (2.3).

P(z) = 2/c )3 Ira)2 cos(27rlz) (2.3)
l

The functions were synthesized from z = 0.0 to 1.0 in increments of 0.01
for all materials.

The signs of the structure factors were directly obtained from the
scattering contributions of the V205 framework. This assumes that the
scattering contribution from the intercalated PEO is relatively small. The
structure factors for the V205 framework alone were calculated as follows.

Atomic scattering factors for vanadium and oxygen were determined by eq
(2.4)

4
f(0) = [)3 a,- exp(—b;}\'2 sinzfl) + c] exp(—B sin20 / A2) (2.4)

i=1

51

Table 2.1. X-ray Diffraction Data and |F(l)|2 for V205-”“20 xerogel

 

d(obsd). d(calcd)- Intensity
<th (A) (A) (count) IF(l)l2
001 11.41 11.41 18566 42.58
003 3.81 3.81 1707 37.08
004 2.86 2.86 552 22.28
005 2.29 2.29 458 30.52
007 1.63 1.64 58 8.73

008 1.44 1.43 54 11.11

52

Table 2.2. X-ray Diffraction Data and (rah2 for (PEO)0,5V205-nHzO

 

d(obsed) d(calcd) Intensity
(hkl) (A) (A) (count) [NW
001 13.22 13.25 28892 49.285
002 6.70 6.63 1820 12.262
003 4.44 4.43 2708 42.617
004 3.33 3.33 1 188 34.381
005 2.67 2.67 997 46.832
006 2.22 2.23 568 40.539
007 1.92 1.91 45 4.548
008 1.66 1.68 93 13.366
009 1.48 1.49 87 16.651
0010 1.33 1.35 31 7.630

 

53

Table 2.3. X-ray Diffraction Data and ”.7012 for (Peonhvzosmnzo

 

d(obsed) d(calcd) Intensity

(bk!) (4) (4) (count) W012

001 16.80 16.86 5.587e+5 588.69
002 8.56 8.45 1.177e+5 481.72
004 4.28 4.25 6.3506+4 1077.40
005 3.42 3.41 3.239e+4 887.83
006 2.84 2.85 2.7386+4 1121.20
007 2.44 2.44 2.323e+4 1333.10
008 2.14 2.14 1.36Se+4 1064.60
009 1.90 1.91 3.000e+3 310.22
0010 1.70 1.72 4.914e+3 667.31
001 1 1.55 1.57 8.049e+3 1368.20
0012 1.43 1.44 3.6356+3 760.91
0013 1.32 1.34 1.258e+3 317.49

 

54

Table 2.4. X-ray Diffraction Data and IF (l)|2 for (PEO)1,5V205-nH20

 

d(obsed) d(ca1cd) Intensity
(hkl) (A) (4) (count) |F(l)|2
001 17.58 17.56 2.269e+6 2181.7
002 8.74 8.75 5.516e+5 2166.2
004 4.27 4.34 2.334e+5 3988.4
005 3.44 3.46 1.184e+5 3188.2
006 2.87 2.88 8.289e+4 3320.5
007 2.46 2.46 8.596e+4 4845.7
008 2.15 2.14 3.434e+4 2640.8
009 1.90 1.90 6.0016+3 617.6
0010 1.71 1.70 5 .954e+3 793.6
0011 1.56 1.54 1.217e+4 2029.3
0012 1.44 1.42 9.2826+3 ‘ 1884.5

 

55

where the values of ai, bf and c for each element were obtained from the
literature.17 B is a temperature parameter and assumed to be 2.0 for every

element. The structure factors were calculated according to eq (2.5)

N
F (l) = 2 2f]- cos(2 nlzj) (2.5)
j=1

where fj is the scattering factor of j atom (obtained from eq (2.4)) and Zj is

its fractional coordinate on the c-axis. Here, Oka's model was used. The

fractional coordinates (Zj) of V and O in the V205 framework are shown in

Table 2.5.

Table 2.5. z Parameters of V and O for the PEO/V205 Compounds

 

z parameter

 

VO1_5 sheet 0 sheet
PEOLonOs-nHzO 0.0833 0.179
PE01,5V205-nH20 0.0796 0.171

 

The F(l)ca1a1 values for PE01,0V205-nH20 and PEO1,5V205-nH20 are
shown in Tables 2.6 and 2.7, respectively. The 1-D electron densities were

obtained from eq (2.6).

p(z) = (1/L) [F0 + 2); F, cos(27rlz)] (2.6)
l

L is the length of the repeat unit and F0 is the zeroth-order structure

factor. The electron densities of the PEO/V205 materials were calculated

56

Table 2.6. Observed and Calculated Structure Factors for
(PEO)1_0V205~nH20

 

(th) IF ( l)|(obsd)* F (1)3(calcd) F (Uflcalcd)
001 10.676 25.662 . 21.970
002 9.657 2.844 9.433
004 14.442 -11.629 —12.311
005 13.110 -17.245 -13.023
006 14.733 -12.758 -15.905
007 16.065 -15.866 -15.581
008 14.357 -10.739 ~10.050
009 7.750 2.463 3.034
0010 11.366 5.745 3.981
0011 16.276 4.248 5.708
0012 12.137 4.224 4.024
0013 7.840 2.586 1.934

 

3 Includes scattering of V205 only. 9 Includes contributions of V205 and
PEO; R = 0.38, K = 0.44. R calculated as R = 2(lKlFol-IFA|)/X(KIF0|).
*Corrected by K.

57

Table 2.7. Observed and Calculated Structure Factors for
(PEO)1.5V205nH20

 

(hkl) |F(l)l(obsd)* F ( l)a(ca1cd) F ( l)b(ca1cd)
001 11.210 30.451 3 19.171
002 11.170 10.002 12.183
004 15.157 -9513 —12.670
005 13.551 41.794 41.794
006 13.830 45.177 43.937
007 16.707 -16.060 45.621
008 12.333 41.003 43.748
009 5.965 -2713 0.647
0010 6.761 3.361 1.197
0011 10.812 5.147 5.626
0012 10.419 4.201 4.731

 

3 Includes scattering of V205 only. 9 Includes contributions of V205 and
PEO; R = 0.293, K = 0.24. *Corrected by K.

by using 1
from the)
0.2 10 I
checked I
(mmhn
amounts

possible

111612
The

61C

58

by using the IF (Ulobsd, obtained from eq (2.1), with the signs, obtained
from the F (Ucalcd . The electron density maps were synthesized from z =
-0.2 to 1.2 in increments of 0.01. The signs of the phases were also
checked by recalculation of the electron densities, including the scattering
contributions of the PEO molecules. In the recalculation, the exact
amounts of PEO molecules (based on elemental analysis) with different
possible conformations and positions were used. Before and after the PEO
molecules were included, the signs of the phases were consistent in the case
of (PEO)1,0V205-nH20, but slightly different in (PEO)1,5V205-nH20.
Namely, one reflection sign changed in (PEO)1.5V2O5-nH20 but this did

not consequently change the ED pattern.

2.2.3. Preparation of V205 Xerogel

V205 xerogel was prepared by a reported method.18 Sodium
metavanadate, 4 g (32.8 mmol) was dissolved in 250 ml of distilled water.
The resulting solution was eluted through a column packed with H+ ion-
exchange resin (Dowex-50X2-100) forming a pale-orange solution HVO3.
Upon standing, the HV03 polymerized to a red V205 gel in several days.

After evaporation of excess water, a film of V205 xerogel was formed.

2.2.4. Preparation of (PEO)xV205-nH20

Aqueous solutions of 0.01 M V205 gels mixed with a stoichiometric
amount of PEO (M.W.= 1x105), were stirred overnight in the dark. The
PEO/V205 molar ratio was varied from 0.5 to 5.0 in increments of 0.5.
The resulting red mixture was cast into a film by evaporation of water at
room temperature on a flat surface without further washing. High

molecular weight PEO (MW = 5x106) was also used and gave rise to

similar in

molecula

2.
A
light so

expose:

inCll
and c
by 8

W611

59

similar intercalation compounds. Most data on this paper were from low

molecular weight PEO.

2.2.5. Photoreaction of (PEO)szOs-nH20
A medium-pressure Hg lamp filtered by Pyrex glass was used as a
light source. PEOszOs-nHzO films coated on a piece of glass slide were

exposed to this light source in air for 12 hours.

2.2.6. Preparation of Liy(PEO)xV2Os-rtH20

An amount of 0.5 g of PEOszOs film reacted with 2 equivalent Lil
in CH3CN for 3 days. The resulting blue product was washed with CH3CN
and dried in air. No trace of iodine or iodide were detected in the product
by SEM/EDS microprobe analysis. The compositions of these materials

were determined by elemental analysis.

2.3. Results and Discussion

2.3.1. Structure of V205 Xerogel

V205 xerogel is a lamellar material with an interlayer distance of
11.5 A- Livage et al. proposed that the V205 layers are composed of
corrugated ribbons with a step of 2.8 A,19 see Figure 2.1a, and the intra-
ribbon structure is closely related to single layers of orthorhombic V205.
Recently, Oka et al. proposed a different structure in which the layers
consist of two V205 sheets facing each other at a distance of 2.8 A
according to the structure of MXVZOSZO (M = Na, K) as shown in Figure
2'19 Most studies reported to date seem to prefer Livage's model.4r19
HoweVer, density measurements for V205-1.08DMSO and

60

.3 00 55 80.... a: :3 00 0w0>§ :25 3 u 0:2:
0: 05 3:: ©3023: Ewes: 0O; .8 00:00.50 008:8: 05 0: 520.502: 0:080:0m Ad 0.53m

: _ o VBEEE

 

<m.N

i
i
i
l

(P1

1110

Slat

Cry:
”M

the

lhtf
01c
aise

layfi

Xtro

61

(PEO)1,0V205-0.7H20, shown in Table 2.8, are consistent with Oka's

model.

2.3.2. Characterization of (PEO),.VzOs-nHZO Phases

A series of (PEO),.VzOs-nHzO nanocomposite intercalates with x =
0.5 to 5.0 were prepared. Depending on x, several phases were identified
by the X-ray diffraction. Figure 2.2 shows typical X-ray diffraction
patterns in which 001 reflections dominate. The phase with x = 0.5 has
been reported with an interlayer spacing of 13.2 A. As x increases , the
interlayer distance increases from 16.8 A at x = 1.0 to 18.3 A at x = 5 as
summarized in Table 2.9. The net V205 interlayer expansion is from 4.5
A at x = 0.5 to 9.6 A at x = 5.0. The coherence length along the layer
stacking direction, as estimated from the Scherrer formula, decreases from
90 A when x = 0.5 to 60 A when x = 4. Scanning electron micrographs of
these PEON205 composites are shown in Figure 2.3. After intercalation,
the surface becomes distinctly corrugated, consistent with the decreased
crystallinity. Compared with V205 xerogel, these composite films show
much improved mechanical flexibility which becomes more noticeable as
the PEO content increases. All of the phases absorb moisture reversibly
which causes a further 2 A expansion in the interlayer distance. However,
these highly hydrated forms of (PEO)xV205-nH20 show poor crystallinity
or consist of mixed phases. Materials with high MW PEO (5.0x106) were
also prepared and they generally show an improved crystallinity in the
layer stacking direction. For example, the coherence length of
(PEO)0.5V205-nHzO increases to 112 A, a value higher than that of V205
xerogel itself.

Even though a large amount of PEO can be intercalated, in fact,

62

Table 2.8. Calculated and Measured Densities for (DMSO)1,03V205 and
(PEO)1,0V205-0.7H20.

Density (g/ cm3)

 

Compound Livage Oka Measured value
V205-1.08DMSO* 1.18 2.35 2.25
(PEO)1,0V205-0.7H20 1.1 ~2.2 ~2.3

 

*Copy from ref 20.

 

55:35

Figure

“)1 (Pl

 

63

 

 

 

 

 

Intensrty

A
C!“

v

 

 

 

AA

TrTIIIIIITITTIrIIIIIITIIUIII

0 10 20 30 40 50 60
2 Theta

 

 

 

Figure 2.2. X-ray powder diffraction patterns of films of (a) V205 xerogel,
(b) (PEO)05VZO5JIH20 and (C) (PEO)15V205-nH20.

64

Table 2.9. Summary of Interlayer Distance, Net Expansion and
Coherence Length for (PEO),.VzOy-nHzO

 

Molar ratio Interlayer distance Net expansion1 Coherence length2

(PEG/v.05) (A) (A) (A)
0* 1 1.5 2.8 100
0.5 13.2 4.5 90
0.8 13.2 4.5 90
1.0 16.8 6.9 88
1.2 17.2 8.5 70
1.4 17.4 8.7 77
1.5 17.6 8.9 75
2.0 17.6 8.9 75
2.5 17.6 8.9 70
3.0 ~18.3 9.6 65
4.0 ~18.3 9.6 60
5.0 ~18.3 9.6 - 60

 

1The thickness of the V205 layer is 8.7 A. 2Along the layer stacking axis.
*V205 xerogel.

a) n is ~1-1.6 for the phases with x < 1 and 0.5-1.0 for the phases with x Z
1.

65

(A)

15KU 81300 0402 10.0U CED92

 

(B)

    

B402 10.0U CEUBE

Figure 2.3..Scanning Electron Micrographs of (a) V205 xerogel
(b) (PE0)0.5V205-nHzO-

SC

(11

an
du
nn
0b
Ht
[ht
1W1

1W1

Chat

66

when the PEON205 molar ratio reaches five, considerable amount of PEO
was found outside the layers as a separated phase. We observed bulk
crystalline PEO by X-ray diffraction. By washing out the excess PEO with
CH3CN, we found that materials with x < 2 show no significant
composition changes by TGA, indicating no Significant amount of un-
intercalated PEO. For x _>_ 2 , after washing, the final product always
shows x in a range of ~2.0. However, washing also decreases the interlayer
spacing from 18.3 A to 17.5 A, for the phases with x > 2.5, implying that
some intercalated PEO might be washed out. Thus, we cannot precisely
determine the maximal PEO loading in the V205 framework from the
CH3CN washing experiments. Ff-IR spectroscopy indicates that an
accumulation of the bulk PEO phase exists from x > 2.

After PEO intercalation, the structural integrity of the V205
framework is maintained as confirmed by the infrared spectroscopic data
and X-ray diffraction. Three strong vibrations at 1010, 750, and 570 cm-1,
due to the framework, and two intense electronic UV/V is transitions at 270
nm and 380 nm, due to the ligand-to—metal electron transfer, were
observed. These values are nearly identical to those of V205 xerogel.18t21
However, the intercalated PEO shows some structural modifications. In
the region of the CH2 stretching absorption, a strong band at 2880 cm'1 and
two weak bands at lower wavenumber observed in bulk PEO, change into
two well-defined bands at 2910 and 2878 cm'l. In the region of 1500 to
1100 cm-1, no significant energy shifts are observed, but the relative
intensities between absorptions are different and the band shapes become
broader. Below 1100 cm‘l, the absorptions are mainly shielded by the
strong vibrations of the V205 framework. These small but significant

changes are due to steric interactions between the confined PEO and the

fitment

B.
on sub:
contains
plane st
that thc
0i V30
intcrcal

structm

67

framework.

Because of the preferred orientation of PEO/V205 composite films
on substrates, X-ray diffraction in the regular reflection mode only
contains the 001 set of reflections. The hk0 set, which derives from the in—
plane structure, can be only observed in the tranSmission mode. We found
that the transmission patterns of all PEONzOs phases are identical with that
of V205 xerogel, as shown in Figure 2.4. This further confirms that the
intercalation is topotactic and does not disrupt the two-dimensional V205

structure.

2.3.3. Structure of (PEO)XV205.nH20

Since a relatively large number of 001 reflections are observed due
to scattering from planes perpendicular to the stacking axis, we attempted
to determine the structure of the intercalated species projected on the c-
axis. This is possible by calculating one-dimensional Patterson functions
and electron-density maps from the observed intensities. Assuming the
structural model for the vanadium oxide part of the structure is known and
correct, the projection of the PEO structure on the c-axis may be
determined from difference electron-density maps. This could yield
specific information about the orientation and structure of the intercalated
polymer, or at least eliminate certain conformational possibilities. The
one-dimensional Patterson functions, calculated from the 001 reflections,
are shown in Figure 2.5 along the layer axis (defined as the c-axis). This
function derives from the projected structure of (PEO)xV205-nH20 on the
c-axis. The 1-D Patterson function of V205 xerogel itself shows two peaks
at 2.8 A and 4.5 A. The strong peak at 2.8 A is assigned to the V-V vector
(projected on the c-axis) from two adjacent V205 layers and the peak at 4.5

Intensity

 

Fig" I'l
Xerog‘

68

 

 

 

(a)
W
(b)
Rec...)
(0)

 

 

 

 

A?
8
E
....,....,.........,.-..,....,
0 10 20 30 40 50 60
2Theta

Figure 2.4. Transmission mode of X-ray diffraction patterns for (a) V205
xerogel, (b) (PEO).,5VZOS-nHZO and (c) (PEO)15VZOS-nHZO.

69

(a)

 

P(z)

 

 

 

0 . 287' '5.75' 863' t 11.5
O» z (A)

 

P(z)

 

 

 

 

P(z)

 

 

 

 

 

f I I I I f

I I l V I' r

o 4.4 88 I 13.2 17.6
z (A)

Figure 2.5. One-dimensional Patterson functions along the interlayer

c-axis of (a) V205 xerogel, (b) (PEO)05V205-nHZO and (3)

(PEO)15V205'HH20.

fur

Fi

lit

70

A is due to the V-O vector involving oxide atoms and water.18<’tl These
PEO intercalates preserve the original peaks associated with the V205
framework and show a new broad peak centered at 6.6 A for
(PEO)(),5V205-nH20 and 8.8 A for (PEO)1,5V205-nH20. Its intensity
gradually increases with PEG loading indicating. that the peak is due to the
vector between vanadium atoms and atoms in PEO. The appearance of
these peaks confirms that the internal structure of the V205 layers is intact
and indicates that PEO is positioned at interlayer regions, not at intralayer
regions. This agrees with the spectroscopic and X-ray diffraction data
which show that the structure of the host is undoubtedly unchanged. This
is important in the following l-D electron density calculations for the
characterization of the PEO conformation

In a previous study we showed that the interlayer expansion as a
function of PEO content does not vary linearly, but shows plateaus, see
Figure 2.6, indicating that the intercalation of PEO is either a layer-by-
layer process or subject to a conformation change from a planar zigzag to a
helix. For example, (PEO)()_5V205-nH20 has a net expansion of only 4.5
A which is too small for a helical structure suggesting that the PEO
conformation must be close to a planar zigzag. However,
(PEO)xV205-nH20 phases with x 2 1 have a net expansion of 8 A or
higher which is compatible either with two layers of polymer chains with a
planar zigzag conformation, or one layer of helical PEO. In order to
probe the polymer conformation, 1-D electron density (ED) maps were
calculated along the layers stacking direction.

Ideally, if PEO has a helical conformation the 1-D ED map along the
c-axis should show a broad peak between the layers, see Figure 2.7a. If

PEO has a planar-zigzag conformation, the 1-D ED map can show several

°<

C" ‘0 ‘i

i

Interlayer distance (A)

71

 

19

18*

17‘

16"

15"

14"

 

 

..l

13 TTIITITITIITIIITTTIIITTI'rTI

0 l 2 3 4 5 6
Molar ratio (x)

 

 

Figure 2.6. Variation of interlayer distance as a function of x for
(PEO)XV205-HH20.

 

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72

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73

patterns which depend on the packing arrangement of the polymer chains.
For example, if the plane containing the zigzag chain is parallel to the
V205 layer, the 1-D ED map should show two peaks symmetrically
disposed from the middle as shown in Figure 2.7b. On the other hand, if
the plane is perpendicular to the V205 sheet, the 1—D ED map should show
4 peaks (Figure 2.88). In this case, the distance between peaks due to a
single polymer chain should be less than 0.9 A. Another possibility is that
the PEO bilayer structure is arranged in a zigzag-like fashion. In this case,
l-D electron density map will also show 4 peaks (Figure 2.8b). Of course,
there are still many possibilities. The 1-D ED calculation of
(PEO)1,0V205-nH20 phase, based on Oka's model, is shown in Figure 2.9.
As expected, the distance of the adjacent V205 planes is ~2.8 A and the
V=O bond is ~1.6 A. Four ED peaks due to PEO are observed between the
layers and the average distance between adjacent peaks is ~ 2.0 A. This
suggests that the intercalated PEO has a zigzag bilayer structure and its
chain conformation is close to a planar-zigzag22 as depicted in Figure 2.8b.
This 9130 conformation is dramatically different from the coil
conformation proposed in systems where the intercalation is based on the
affinity of PEO toward alkali ions. An attempt to produce helical PEO by
additional incorporation of Li salt such as LiClO4 and LiCF3SO3 in the
preparation did not succeed. Based on the X-ray diffraction, the product is
a mixture of V205 and/or PEONzOs as well as a Li salt complex with
PEO. At low PEO levels, we believe that the driving forces for PEO/VzOs
stabilization are van der Waals interactions and hydrogen bonds which are
maXimized when the polymer is fully extended (i.e. zigzag conformation).
The 1-D ED map of (PEO)1_5V205~nH20 was also calculated and shows a
similar pattern with (PEO)1,0V205-nHzO, indicating that the intercalated

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74

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76

PEO molecules still have a double layer arrangement. The ED calculations
of the phases with x > 1.5 are not reliable due to low crystallinity and
insufficient numbers of observed reflections. Thus, the PEO intercalation
is a layer-by-layer insertion without any conformational change from a

zigzag to a helix.

2.3.4. Photoreaction of (PEO)XV205-nH20

The (PEO)xV205onH20 materials are light-sensitive and turn blue
when they stand in room light for several weeks. Exposure to a medium-
pressure Hg lamp causes the materials to turn blue in an hour. The color
change is due to a light-induced redox reaction in which the PEO is
oxidized by the vanadium oxide framework. The infrared spectra of
irradiated samples show a new very weak absorption around 1700 cm-1,
indicating that the PEO molecules probably are oxidized to aldehyde or
even acid. The vibration of V=O slightly shifts down to ~ 1000 cm-1,
consistent with increased number of V4+ centers.23 Except for these, we
do not observe significant changes in the position and shape of infrared
absorption peaks of the PEG and vanadium oxide framework, suggesting
only minor structural changes in the framework. The irradiation slightly
decreases the interlayer spacing, see Table 2.10, due to some water
expulsion from the layers caused by the reduction of the V205 framework
which make it more hydrophobic.

The redox nature of the photoreaction is confirmed by the increased
magnetic susceptibility and enhanced intensity of the material's EPR signal.
Figure 2.10 shows variable-temperature magnetic susceptibility data for
fresh and irradiated samples in which the irradiated material shows a

higher value than the fresh material. This confirms more V4+ centers in

77

Table 2.10. X-ray Diffraction and Magnetic Data of Irradiated
(PEO),,VzO5-nH20 Compounds

 

d-spacing EPR Heffl )((T1p)lL
x Color decrement (A) (gauss) (BM) (emu/mole)
0.5 blue 0.2 400* 0.73 1.28x104
1.0 blue 2.2 hyperfine 0.81 1.55x104
1.5 blue 1.2 hyperfine 0.77 1.36x104

 

*Peak-to-peak width.
TTIP: Temperature Independent Paramagnetism.
lpeff was calculated from X(Curie-weiss) component.

(mole/emu)

1

X

8000

7000

5000

4000'

3000
2000
1000

78

 

(b) a

I I fij r I Trj I I

.. .,. ., ......,
0 50 100 150 200 250 300
Temperature (K)

  

 

 

Figure 2.10. Magnetic susceptibility of (a) fresh and (b) irradiated
(PEO)0.5V205-nH20 as a function of temperature.

79

the framework upon irradiation. The magnetic susceptibility (an)
decreased with rising temperature but there is no linear relationship
between the inverse Xm and temperature. We found that the magnetic
behavior can be interpreted as Curie-Weiss type with a small amount of
van Vleck temperature-independent paramagnetism (TIP),24 shown in
Figure 2.11. The un-irradiated PEO/V205 compounds have an average
ueff (calculated from X(Cun‘e-Weiss)) of ~0.3-0.4 BM at room temperature.
After 12 h of irradiation, the ueff increases to 0.7-0.8 BM because of the
increased V4+ concentration, see Table 2.10.

Before irradiation, the EPR hyperfine structure is observed in the
spectra of PEO/V205 materials due to (V=O)2+ impurities (S=1/2, l=7/2)
in an axially distorted crystal field.25 After irradiation, for example in
(PEO)0,5V205-nH20, the increased V4+ concentration causes a gradual
disappearance of the original hyperfine splitting and a gradual appearance
of a broad peak (due to V4+-V4+ exchange interactions) as shown in Figure
2.12. The g value is ~1.96. Surprisingly, this is not the case in
(PEO),,VzOstzO materials with x Z 1. Even though the flair of the PEO-
rich materials is slightly higher than that of PEOO5V205-nH20, indicating
higher V4+ concentration in the former, the EPR hyperfine structure still
persists, suggesting that the average V4+ concentration in the PEO-rich
materials is lower than that in (PEO)0.5V2O5-nH20. One possible
explanation for this is that some of V“ centers, probably in the form of
V02+, diffuse between the layers and are magnetically isolated by
coordination to PEO. The existence of V02+ species has been proposed in
the reduced V205 xerogels.26

Optical diffuse reflectance spectra of the irradiated materials contain

a new very broad absorption band centered at 1400 nm, see Figure 2.13,

-1

X (mole/emu)

 

80

 

(b)
(C)

 

 

 

0 ...I-...,....,....,....,....,....
O 50 100 150 200 250 300 350
Temperature (K)

Figure 2.11. Inverse magnetic susceptibility of irradiated
(PEO)05V205-nH20 as a function of temperature : (a) xm, (b)

x(Curie-Weiss) and (C) X(measured)- (X(measured) = X(Curie-Weiss) + Xcrrm)

81

(b)

 

 

2006

I
34006

Figure 2.12. Room temperature EPR spectra of irradiated (a)
(PEO)o,sV2Os-nH20 and (b) (PEO)1,5V205-nH20.

82

 

 

 

 

 

 

 

 

Q)
a
—§
0
.8
<1
I I I T I I I I I I I l fi I I
200 775 1350 1925 2500
nm

Figure 2.13. Optical absorption spectra of un-irradiated (a) and
irradiated (b) (PE0)05V205°HH20.

83

which is due to an intervalence electronic transition associated with the
mixed valence V4+IV5+ framework.27 The appearance of this band is
consistent with the increased number of V4+ centers in the V205
framework and indicates charge transfer from the polymer to the V205

framework.

2.3.5. Charge Transport Properties

The irradiated samples show diminished solubility in water and
enhanced electrical conductivity as listed in Table 2.11. The irradiated
(PEO)0,5V2Os-nHzO has nearly two orders magnitude increased
conductivity, up to 10'2 S/cm at room temperature. The irradiated
(PEO)1.5V205-nHzO has a lower conductivity of 5x104 S/cm, probably
because of the increased spatial separation of the conductive V205 layers
which increases the barrier of electron transport through the material. The
conductivity as a function temperature is shown in Figure 2.14a and is
consistent with a thermally activated charge transport as in many small—
polaron conductors,28 where the transport is due to carriers hopping.
Thermoelectric power data, shown in Figure 2.14b, confirm the non-
metallic nature of these systems. The Seebeck coefficients are negative with
large values and decrease with falling temperature. This indicates n-type
thermally activated charge transport. The Seebeck coefficient of
(PEO)0,5V205'nH20 is less negative than those of the PEO-rich materials,

consistent with the higher conductivity of the former.

2.3.6. Alkali Ion Intercalation
As mentioned above, the intercalation of PEO does not change the

structure and electronic state of V205 framework. In other words, the

84

Table 2.11. Room Temperature Electrical Conductivity and
Thermoelectric Power of Unirradiated and Irradiated (PEO)xV20s-nHzO

 

 

 

Materials
ConductivitLo (S/cm) Thermopower (uV/K)
x Un-irradiated Irradiated Irradiated
0.5 104 10*2 -140
1.0 10‘5 10‘3 -150

1.5 10*5 5x10‘4 -160

85

 

 

 

 

 

 

 

 

 

(A)
’2;
i
-4; A
A L
E .
Q -50
(‘0’ P
0 C
-3_
§’ . D
.. O
-10L ° 0
r
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2 4 6 8 10 12
1000/r (K‘)
(B)
-100
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-140— 0 °
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3 ‘180"% Q go
3 I ‘85 09%
S: -220— f
E ~ 0
’260? 000
-300Pg...i....i....1...#
15 200 250 300 350

Temperature (K)

Figure 2.14. (a) Four-probe variable temperature electrical conductivity data
of films of irradiated (i) (PEO)o,5V205-nH20 and (ii) (PEO)1,5V2Os-nH20,
and (b) Thermoelectric power data of . films of irradiated (i)
(PEO)o,5V205-nH20 and (ii) (PEO)1,oV2Os-nH20.

86

PEO/V205 compounds preserve the oxidation ability of the V205
framework and thus are good hosts for further redox intercalation. By
reaction with lithium iodide, we are able to intercalate lithium ions to the

PEO/V205 phases according to eq (2.7).

)4.“ + (PEO)XV205"2H20

 

V Liy(PEO)xV205'mH20 + y/2 12 (2.7)

The redox intercalation reduces the V205 framework and produces iodine
as a byproduct which is detected spectroscopically. The reduced
framework acquires a blue color and increased magnetic susceptibility.
The infrared spectra of Liy(PEO)xV2Os-nHzO compounds show no
significant changes from those prior to intercalation. The compositions
and X—ray diffraction data of the Liy(PEO)xV2OsonHzO compounds are
listed in Table 2.12. The intercalation decreases the interlayer distance and
the crystallinity in the c crystallographic direction. For example, the
average coherence length decreases by 15 A to 60-70 A. Regardless of y in
Liy(PEO)o.5V205-nHzO compounds, the net interlayer height is always
much less than 8 A, which is the expected van der Waals diameter of a
PEO helix containing Li+ cations. This suggests that the incorporation of
Li+ ions does not change the conformation of PEO from a zigzag to a
helix. This is possible that the Li+ ions are solvated by hydrated water and
do not bind to PEO or that the bonding mode between the PEO and the Li”
ions must be such that a coiled structure is avoided. However, the net
expansion of 7.7 A in the Liy(PEO)1,5VzO5.nHzO implies that the PEO
may either preserve the double zigzag conformation or change to a coiled
structure in the presence of Li+ ions. The Li+ intercalated products do not

show a sufficient number of 001 reflections in the X-ray pattern to warrant

87

Table 2.12. Composition, Net Expansion and Coherence Length of
My(PEO)xV205.-nHzO

Coherence Length

 

Net interlayer (along c-axis)
x M y eyansion (A) (A)
0.5 Li 0.18 4.3 76
1.0 Li 004* 5.4 46
1.5 Li 0.17 7.7 60

 

*Prepared by using large pieces of PEONzOs films and no stirring during
the reaction.

88

a meaningful electron density calculation as was done in the case of
PEONzOs above. Thus, the conformation of PEO and the chain
arrangement in Liy(PEO)xV20sonHzO could not be probed by this
technique.

2.3.7. 7Li NMR Studies

The Liy(PEO)xV2Os-nHzO materials were examined with variable
temperature wide-line 7Li NMR spectroscopy in the hope of probing the
state and coordination of Li” in the galleries. Regardless of the Li’r or
PEO content, the samples showed just one signal of first order quadrupolar
transition with no significant satellite peaks. The change in width at half
height (Am/2) versus temperature for different samples is shown in Figure
2.15. In general, a similar trend of a decrease in A010 with increasing
temperature is observed in all samples. Typically, Avl/z decreases
gradually but slowly with increasing temperature, and then a significant
narrowing of the lines are observed in the temperature range of 220 to 320
K, after which the line narrowing again gradually increases. As long as the
temperature remains below 350 K, above which the vanadium oxide
framework begins to decompose, this behavior is reversible for many
cooling and heating cycles.

The range of change in Av1/2 with increasing temperature is
influenced by the amount of PEO in the layer. Even though all the
intercalates studied with or without PEO behave similarly, where line
narrowing of the signals takes place with increasing temperature, the
sample with the lowest PEO load, Li0.13(PEO)0.5VzO5°nHzO, shows the
highest width in the lower temperature region (< 240 K). The one with the
highest PEO load but with about the same amount of Li,

89

 

20
A : k A

16': B
an I
a '1
0
a: 81 \
+5 . C \
5. 4‘.
3 J D

o . .

 

 

 

..,...,...,..T...
180 220 260 300 340 380

Temperature (K)

Figure 2.15. Width at half height versus temperature of 7Li NMR signals
for samples, (A) Lio.1s(PE0)o.sV205°”H209 (B) Liozvzos'nH209 (C)
Lio.o4(PE0)1.oV205'"H20, (D) 1410MP E0)15V205onH20.

90

Li0.17(PEO)1.5VzO5-nll20, shows a much narrower signal at < 240 K
studied. Though both samples have similar Av1/2 at 280 K, at higher
temperatures, the situation is reversed and the sample with the highest PEO
shows a higher Avl/z. In both cases the signals are symmetric with no
indication of different lithium environments at all temperatures studied.
This observation may suggest that the sites that the Li ions can occupy in
the general framework are very much affected by the presence of PEO
which also imposes limitations on their mobility probably via coordination.
The sample with an intermediate PEO load but with the lowest lithium
content Li0.04(PEO)1_0V205-nH20, shows an intermediate line narrowing
in the low temperature region. Thus below ca 280 K regardless of the
amount of lithium load, the higher the PEO content the wider the signals.
The lithium in these samples can either be coordinated exclusively to PEO
or be in a mixed PEO/water environment or it may exist in two different
environments, one exclusively coordinated to PEO and one exclusively
coordinated to water. Of course, it is also possible that framework oxide
ions may be involved in Li+ coordination, although we believe this is
unlikely when PEO and water are also present. The distribution of these
different Li+ environments would depend on the PEO and water contents
in the material. For example, low PEO contents may not be sufficient to
fully complex the Li+. Distribution of the Li+ sites may also depend on the
temperature. For example, at higher temperature a more homogeneous
lithium environment may be achieved through thermal equilibration and
ion hopping. The fact that we observe only one signal suggests, but does
not prove, that the Li“ ions are primarily in one type of environment. The
materials exhibiting asymmetric 7Li-NMR lines may indeed contain

substantial number of lithium ions in different sites. For the purpose of

91

comparison, we examined Li02V205-nH20 (no PEO) which contains the

highest load of Li+. The spectrum of this material undergoes a similar line
narrowing with increasing temperature, see Figure 2.15. Interestingly, this
sample with the highest lithium content shows a signal with a broader base
at all temperatures, perhaps suggesting different Li+ sites. With increasing
temperature a significant amount of asymmetry is also observed while the
broader base is also retained. With the most reduced state of the V205
layer, the asymmetry of the signals in this sample is an indication of
symmetrical Li+ environments overlapping with some unsymmetrical sites
which induce an electric field gradient (efg) around the Li nuclei. The
substantial line narrowing observed in the spectra of all materials with
increasing temperature is also consistent with enhanced ion mobility and
ion-conductivity in these systems. Ion mobility will lead to changes in the
local movement of the Li‘“ ions. An increase in temperature presumably
leads to an increase in the mobility or exchange frequency of lithium. A
similar observation of line narrowing of lithium NMR signals with
increasing temperature has been reported earlier for (PEO)8LiClO4 and
Li1+xV3Og.29 Furthermore, other qudrupolar nuclei like sodium, when
complexed to PEO, have been shown to undergo a similar line narrowing
transition with temperature.30

The spin lattice relaxation time T1 at room temperature measured by

the spin recovery technique shows 117 ms for Li0.13(PEO)0.5V205~nHzO
and 131 ms for Li0.17(PEO)1.5V205-nH20. These Tl values are in the
same range with values reported earlier for Li salts of PEO.31 The larger
T1 in the latter material suggest that the relaxation of lithium in the layer is
also influenced by the amount of PEO in the layer and may reflect a more

extensive coordination of lithium by PEO.

92

Attempts to extract chemical shift information for different samples
were mostly inconclusive mainly because of the extremely wide signals (in
the range of KHz). Yet at room temperature, a recognizable trend of

chemical shift variations were observed for the samples with different

reduced states of the V205 layer. The sample with the maximum load of
Li+ and, hence with the most reduced V205 layer, shows the most up-field

Li chemical shift of ca -25 ppm (compared to LiCl value of 0). Likewise
the sample with the least Li’r content shows the most down-field Li
chemical shift of ca -7.6 ppm., while the one with an intermediate load of
Li+ shows a chemical shift of -14 ppm. It is to be noted that the signals
observed here are symmetric singlets with no indication of significantly
different Li+ environments which would be evident if some of the lithium

were associated with just PEO and some with water or V205.

Furthermore, the trend of chemical shift change with degree of reduction

of the V205 layer is probably due to paramagnetic contact or pseudo-

contact shifts exerted on the Li” nucleus.

2.4. Conclusion

A variety of new PEO/V205 nanocomposite phases have been
obtained. The use of water-swellable V205 gels as a host material has
opened a way for intercalation of water-soluble polymers. The
intercalation of poly(vinylpyrrolidone) (PVP), poly(propylene-glycol)
(PPG) and methyl-cellulose in V205 xerogel have been reported earlier.6b
The intercalation of PEO to V205-121120 xerogel produces new materials
with interesting lithium redox intercalation and photochemical properties.

The photochemical properties are similar but not identical to those in other

93

polymer/V205 systems. For instance, although all polymer/V205 systems
are sensitive to light, the sensitivity decreases in the order of PPG > PEO ~
methyl-cellulose > PVP. The magnitude of increase in electrical
conductivity upon irradiation is associated with~ polymer loading. The
findings can lead to the production of inclusion compounds with controlled
light sensitivity and electrical conductivity.

We have prepared several Liy(PEO)xV2Os-nHzO phases and studied
them by 7Li NMR spectroscopy. Although the results do not prove that the
Li’r ions are coordinated by PEO, lithium ions appear to be mobile at
higher temperature which could impart good ionic conductivity to the

composite materials.

LIST OF REFERENCES

(1)

(2)

(3)

(4)

(5)

94

LIST OF REFERENCES

(a) Giannelis, E.P. in press " Materials Chemistry .° An Emerging
Subdiscipline". (b) Yano, K.; Usuki, A.; Okada, A.; Kurauchi, T.;
Kamigaito, O. Polymer Preprints, 1991, 32, #1, 65. (c) Okada, A.;
Fukumori, K.; Usuki, A.; Kojima, Y.; Kurauchi, T.; Kamigaito, O.
Polymer Preprints, 1991, 32, #3, 540.

(a) Day, P.; Ledsham, R.D. Mol. Cryst. Liq. Cryst. 1982, 8_6, 163-
174. (b) Tieke, B. Mol. Cryst. Liq. Cryst. 1983, 93, 119-145. (c)
Pillion, J.E.; Thompson, M.E. Chem. Mater. 1991, 3, 777-779. ((1)
Enzel, P.; Bein, T. Chem. Mater. 1992, 4, 819-824.

(a) Kanatzidis, M.G.; Tonge, L.M.; Marks, T.J. J. Am. Chem. Soc.
1987, 1%, 3797-3799. (b) Kanatzidis, M.G.; Wu, C.-G. ; Marcy,
H.O.; Kannewurf, C.R. Adv. Mater. 1990, 3, 364-366.

(a) Bouhaouss, A.; Aldebert, P. Mater. Res. Bull 1983, 18, 1247-
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J.C. J. Chem. Soc., Far. Trans 198 9, 86, 4167-4177. (c) Masbah, H.;
Tinet, D.; Crespin, M.; Erre, R.; Setton, R.; Van Damme, H. J.
Chem. Soc. Chem. Commun, 1985, 935-936. ((1) Erre, R.; Masbah,
H.; Crespin, M.; Van Damme, H.; Tinet, D. Solid State Ionics, 1990,
37, 239-251.

(a) Kanatzidis, M.G.; Wu, C.-G.; Marcy, H.O.; Kannewurf, C.R. J.

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Am. Chem. Soc. 1989, _1_11, 4139-4141. (b) Wu, C.-G.; Kanatzidis,
M.G.; Marcy, H.O.; DeGroot, D.C.; Kannewurf, C.R. Polym. Mat.
Sci. Eng. 1989, 61, 969—973. (c) Kanatzidis, M.G.; Wu, C.-G.;
Marcy, H.O.; DeGroot, D.C.; Kannewurf, C.R. Chem. Mater. 1990,
191,222-224. '

(a) Liu, Y.-.I.; DeGroot, D.C.; Schindler, J.L.; Kannewurf, C.R.;
Kanatzidis, M.G. Chem. Mater. 1991, 3, 992-994. (b) Liu, Y.-J.;
DeGroot, D.C.; Schindler, J.L.; Kannewurf, C.R.; Kanatzidis, M.G.
Adv. Mater. 1993, 5(3), 369-372.

Polymer Electrolyte Reviews McCallum, J.R., Vincent, C.A., Eds.;
Elsevier Applied Science: London, 1987 and 1989 Vols. 1, 2.

(a) Ruiz-Hitzky, E.; Aranda, P. Adv. Mater. 1990, 2, 545-547. (b)
Ruiz-Hitzky, E.; Aranda P.; Casal, B. J. Mater. Chem. 1992, 2(3),
581-582. (c) Aranda, P.;Ruiz-Hitzky, E. Chem. Mater. 1992, 4,

1395-1403.

Lagadic, 1.; Léaustic, A.; Clement, R. J. Chem. Soc. Chem.
Commun. 1992, 1396-1397

Bissessur R.; Kanatzidis, M.G.; Schindler, J.L.; Kannewurf, C.R. J.
Chem. Soc. Chem. Commun. 1993, 1582-1585.

Ruiz-Hitzky, E.; Jimenez, R.; Casal B.; Manriquez, V.; Ana, A.S.
Adv. Mater. 1993, 5110), 738-741.

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Klug, H.P.; Alexander, L.E. "X-ray Difi‘raction Procedures for
Polycrystalline and Amorphous Materials "; John Wiley & Sons: New
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Boudreaux, E.A.; Mulay, L.N. "Theory and Applications of
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Lyding, J.W.; Marcy, H.O.; Marks, T.J.; Kannewurf, C.R. IEEE
Trans. Instrum. Meas. 1988, 32, 76-80.

Marcy, H.O.; Marks, T.J.; Kannewurf, C.R. IEEE Trans. Instrum.
Meas. 1990, 3_9, 756-760.

(a) Wendlandt, W. W.; Hecht, H. G. "Reflectance Spectroscopy",
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"International Tables for X-ray Crystallography", The Kynoch
Press, English, 197 4.

Lemerle, J.; Nejem, L.; Lefebvre, J. J. Inorg. Nucl. Chem. 1980,
42, 17-20.

(a) Legendre, J.-J.; Aldebert, P.; Baffler, N.; Livage, J. J. Colloid
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(a) Yao T.; Oka,Y.; Yamamoto, N. Mat. Res. Bull. 1992, 21, 669-
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Abello, L.; Husson, E.; Repelin, Y.; Lucazeau, G. J. Solid State
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Ruiz-Hitzky, E.; Casal, Blanca J. Chem. Soc., Faraday Trans. 1,
1986, 32, 1597-1604.

(a) Drago, R.S. "Physical Methods in Chemistry" W.B. Sanders Co.:
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Sanchez, C.; Babonneau, F.; Morineau, R.; Livage, J.; Ballot, J.
Philos. Mag. B, 1983, 3, 279-290.

Babonneau, F.; Barboux, P.; Josien, E.A.; Livage, J. J. Chim.
Physique 1 985, 82, 761-766.

(a) Bullot, J.; Cordier, P.; Gallais, O.; Gauthier, M. J. Non-Cryst.
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Non-Cryst. Solids 1990, _l_2_1, 35-39.

Bullot, J.; Cordier, P.; Gallais, O.; Gauthier, M.; Livage, J. J. Non-
Cryst. Solids 1984,6_8, 135-146.

(a) Wang, G.; Roos, J.; Brinkmann, D.; Pasquali, M.; Pistoia, G. J.
Phys. Chem. Solids, 1993, 34, 851-855. (b) Gang, W.; Roos, J.;
Brinkmann, D.; Capuano, F.; Croce, F.; Scrosati, B. Solid State
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2208-2209.

Greenbaum, S. G. Solid State Ionics, 1985, 13, 259-262.

Sondregger, M.; Roos, J.; Mali, M.; Brinkmann, D. Solid State
Ionics, 1992, 3, 849-852.

CHAPTER III

INTERCALATION OF V205 XEROGEL WITH
POLY(V IN YLPYRROLIDONE), POLY(PROPYLENE-GLYCOL)
AND METHYL-CELLULOSE

99

100

ABSTRACT

Intercalation of poly(vinylpyrrolidone) (PVP), poly(propylene-glycol)
(PPG) and methyl-cellulose in V205 xerogel is reported. The polymer/V205
intercalation compounds were synthesized by mixing the polymers with
V205 xerogel in water. The products are obtained after water evaporation,
as red composite films. Different composite phases of varying
polymeerO5 ratios can be produced. All polymer/V205 materials are light
sensitive. Upon exposure to a medium-pressure Hg lamp filtered by Pyrex
glass, the red composites turn blue in several hours. This light-induced
redox reaction which results in increased number of V4+ in the vanadium
oxide framework results in the increased number of charge carriers and leads
to higher electrical conductivity in these materials. This change can be

monitored by EPR and magnetic susceptibility measurements.

101

3.1. Introduction

In recent years, the synthesis of new polymer/inorganic intercalation
compounds has attracted considerable interest1'4. In the previous chapter,
we have shown that PEO can be intercalated into V205 xerogel5,6 and
phases with varying PEO loading can be readily prepared by simply
changing the stoichiometric ratios. Further exploration shows that, besides
PEO, other water-soluble polymers such as poly(vinylpyrrolidone) (PVP)7,
poly(propylene-glycol) (PPG)7 and methyl-cellulose7, can be similarly
intercalated into V205 xerogel. We found that the intercalated polymer
content, the interlayer distance, and the photo-sensitivity of the products
strongly depend on the particular polymer. In this chapter, we describe the
synthesis of several new polymeerOs intercalation compounds, their

chemical and physical properties and we compare them to the
PEO/V205.nHzO materials.

3.2. Experimental

3.2.1. Materials

Poly(vinylpyrrolidone), with molecular weight (MW) of 104,
poly(propylene glycol), with MW of 103, and methyl-cellulose, with MW of
6.3x103, were purchased from Aldrich Co., Milwaukee, WI and were used

without further purification.

3.2.2. Physicochemical Methods

See chapter two.

102

3.2.3. Preparation of V205 Xerogel

See chapter two.

3.2.4. Preparation of (polymer)xV2O5.nH2,O Intercalation

Compounds 1

The preparation of the polymerN205 materials was carried out by
mixing aqueous polymer solutions with a V205 solution in various
stoichiometries. The polymer/V205 molar ratios varied from 0.5 to 5.0 for
PVP, 0.5 to 3 for PPG, and 0.05 to 0.5 for methyl-cellulose. The average
increment of the molar ratio is 0.5 for the first two polymers and 0.1 for the
last polymer. The resulting mixture was stirred at room temperature for
several hours and then poured onto a flat surface. After slow water
evaporation at room temperature, a red film was formed. All manipulations
were done with as much exclusion of light as possible. The fresh films are
soluble in water. The water content n (analyzed by thermogravimetric
analysis) is ~0.4-0.5 for PVP, ~0.2—0.4 for PPG, and ~0.3-0.6 for methyl-

cellulose.
3.2.5. Photo-reaction

The (polymer)xV2Os.nHzO were irradiated as described in chapter

two.

3.3. Results and Discussion

3.3.]. Characterization of (polymer)IV2Os Phases

103

Poly(vinylpyrrolidone)

A series of new phases of (PVP)XV205-nHzO were prepared. These
phases are characterized by the different interlayer distances in the V205.
When the molar ratio x was less than 1, mixed phases were found. For
example, when x = 0.2, the d-spacing is the same as vanadium oxide (i.e.
11.5 A) with a shoulder at low 20 angle. When x = 0.5, two phases with
interlayer separation of 19.7 A and 14.3 A were found. However, when x ..
l, a single phase, based on X-ray diffraction, was obtained with an interlayer
spacing of 22.4 A, as shown in Figure 3.1. Three strong (001) diffraction
peaks were observed, consistent with a lamellar nature. As x increases, the
interlayer distance increases from 22.4 A when x = 1 to 43 A when x = 5 as
shown in Figure 3.2. The net V205 interlayer expansion is from 13.66 A at
x = 1.0 to 29.13 A at x = 3.0. The crystallinity (1.e. long range order) of the
composite decreases as the polymer loading increases. The coherence
length along the layer stacking direction, as estimated from the Scherrer
formula, decreases from 57 A when x = 1.0 and 45 A when x = 3. All of the
composite phases are red in color as the V205 xerogel. The infrared
spectrum of intercalated PVP exhibits a significant shift in the C=O
vibration from 1670 cm“1 to 1640 cm'1 which we ascribe to hydrogen
bonding with co-intercalated water3- Compared with V205 xerogel, these

composite films are more brittle.

Poly(propylene-glycol)

In the (PPG)szOs-nHzO system, we observed only two types of
interlayer distances despite the several x values examined. A typical X-ray
diffraction pattern with x = 0.5 is shown in Figure 3.3. The interlayer

distance is 16.87 A when x = 0.5 and increases to 17.7 A when

104

 

 

 

 

 

 

”(001)
A? (002)
(I)
t:
.93
s:
t—t
/ (003)
IITfiIITIlIIIIIFIIITIIIIITFIII
O 5 10 15 20 25 30

20

Figure 3.1. X-ray diffraction pattern of (PVP)1,0V205-nHZO film .

Interlayer distance (A)

105

 

45 .
40-3
354.

 

10 i?
5 l
0 1 2 3 4

x (molar ratio)

Figure 3.2. Variation of the interlayer distance as a function
0f X for (PVP)vaO§°IIH20.

 

1 I I I I I I I I l I I I firr I I I l I I I I

Intensity

106

 

 

 

 

 

 

 

“(001)
(002)
(004)
M
IIfiITIIIIerFIIIITIrTIIIIIIrr
0 5 10 15 20 25 30

20

Figure 3.3. X-ray diffraction pattern of (PPGIosszs-nHZO film.

107

x = 2.0. At higher polymer loading it remains constant as shown in Figure
3.4. The net expansion varies from 8.17 A at x = 0.5 to 9.26 A at x = 3.0
consistent with the presence of only two phases. The coherence length
perpendicular to the stacking direction decreases from 92 A at x = 0.5 to 78
A at x = 3.0. Infrared spectroscopy suggests that PPG retains its chemical
identity in the V205 layers. Compared with V205 xerogel, these composite

films are similar in texture as the one described above.

Methyl-cellulose

Various intercalate phases could also be prepared using methyl-
cellulose. X-ray diffraction of (methyl-eellulose)0,05V205-nHzO is shown in
Figure 3.5. The interlayer spacing increases from 14.02 A when x = 0.05 to
18.3 A when x = 0.35 as shown in Figure 3.6. The net expansion varies
from 5.32 A at x = 0.05 to 9.6 A at x = 0.35. The coherence length
perpendicular to the layers decreases from 71 A when x = 0.05 to just 38 A
when x = 0.35, suggesting a lower degree of stacking order in the polymer-
rich phase. Infrared spectroscopic data of the intercalated methyl-cellulose
are similar to those of the free polymer. The only difference is the vibration
at 947 cm-1 which shifts to 910 cm-1. This vibration was assigned to the C—
H deforrnation of methyl groups"). However, both absorptions co-exist at x
> 0.2. Unlike the materials described above, all phases of methyl-cellulose
are mechanically flexible.

In order to probe the internal structure of the V205 layers in these
compounds, we performed X—ray diffraction experiments with the main
beam perpendicular to the layers (transmission mode). As shown in Figure
3.7, the X-ray diffraction patterns of the inclusion products are identical to

that of pristine V205 xerogel confirming that the intralayer

Interlayer distance (A)

108

 

 

 

 

 

17.7
1 f %——C—4
17.5"
17.3-
17.1“
16.9 ....,....,....,....,rf..I...
0.0 0.5 1.0 1.5 2.0 2.5

x (molar ratio)

3.0

Figure 3.4. Variation of the interlayer distance as function of x
for (PPG)XV205-nH20.

Intensity

109

 

(001)

:3.-

 

 

 

 

 

 

 

10 15 20 25 30
20

Figure 3.5. X-ray diffraction pattern of
(methyl-cellulose)0.05V205-nHZO film.

Interlayer distance (A)

110

 

 

 

 

 

rr

...,. .,.-..,.fi.
0 0.1 0.2 0.3 0.4
x(molarratio)

Figure 3.6. Variation of the interlayer distance as a function of
x for (methyl-eellulose)xV205-nHZO.

 

0.5

Intensity

111

 

(a)

 

(b)

 

 

 

 

-...1....,....,0...,....,....1
0 10 2o 30 40 50 6O
20

Figure 3.7. Transmission-mode X-ray diffraction patterns of films of
(a) (methyl-cc]lulose)o.05V205.nHZO, (b) (PVP)1.0V20511H20 and (c)
V205 xerogel.

112

framework of V205 is structurally preserved9. This is also consistent with
infrared data which show that the characteristic stretching vibration peaks of
the vanadium oxide framework (1014, 750, 496 cm“1 respectively)10 are
present in all compounds.

Thin films of the polymer/V205 composites (coated on quartz slides)
showed two optical absorption bands at 380 and 260 run, again, identical to
that of pristine VzOsrnHzO films“. A typical absorption spectrum is shown
in Figure 3.8. The above data confirm that the compounds reported here are
true inclusion compounds with no significant interaction or charge transfer
between the host and the guest. The constant interlayer distance of the
materials with PPG and methyl-cellulose at high x values may indicate that

some polymer molecules are outside the layers.

3.3.2. Photo-sensitivity

A characteristic property of these composites is their response to light,
particularly of the PPG system. When the red PPG/V205 films are exposed
to room light, their surface turns green within two days. On the other hand,
the color change for the other two polymers takes several weeks. However,
exposure of these materials to a medium-pressure Hg lamp (filtered by
Pyrex glass) dramatically changes the red color to blue in several hours with
the PPG/V205 showing the faster response. The slowest response was
exhibited by the PVP. This blue color is due to a light-induced redox
reaction where the polymers presumably are oxidized by the vanadium
oxide, mentioned in the PEON205 system. For instance, the C-O bond of
PPG is probably cleaved and oxidized to aldehyde or even acid, a process

which releases at least two electrons to

1.5

absorbance

0.5

0.0

113

 

 

 

 

 

E 260nm
_: 380nm
3
'1
I I I I I I T I I I I I F I I
200 425 650 875 1 100
n m

Figure 3.8. Absorption spectrum of (PVP)1_0V205.nH20 film
(transmission mode).

114

the V205 framework. The charge on V205 is presumably balanced by
protons. The infrared spectra of the irradiated compounds show no
significant changes suggesting that most of the polymer remains intact and
that the number of oxidation sites remains small.) However, the formation of
V4+ atoms by this process can be easily detected by EPR spectroscopy and
magnetic susceptibility measurements. As the irradiation time increases, the
EPR signal intensity increases and the original hyperfine structure from 51V
(I = 7,2) nucleus gradually weakens, yielding a new broad resonance in
(methyl-cellulose)0,05V205.nHzO as shown in Figure 3.9. The g value is
1.96 and the broad resonance is about 150 G which is due to the exchange
interaction of V4+ centerslzal‘l. However, the hyperfine structure still
persists in polymer-rich materials such as (PVP)3V205.nH20 and (methyl-
cellulose)0,35VzO5.nHzO. This phenomenon has already been explained in
the PEO/V205 system. This may be due to some of (V=O)2+ centers
diffusing between the layers and becoming magnetically isolated by
polymers, stabilized by coordination either to oxygen atoms in the polymers
and/or water molecules.

The increase in the number of spins is also confirmed by the magnetic
susceptibility measurement as shown in Figure 3.10, where the irradiated
samples show much higher magnetic susceptibility. The fresh sample is
paramagnetic due to the presence of V4+ impurities. The paramagnetic
behavior can be interpreted as a Curie-Weiss type with a small temperature
independent Van Vleck paramagnetism (TIP). The TIP term is originated
from the second order Zeeman effect13 which will be explained in chapter
four. The spin-only effective magnetic moment (ueff, calculated from the
Curie-Weiss component) and X(T]p) of several materials are summarized in

Table 3.1 . The Heff increases from O.3~0.4

115

( methyl-cell ulose)o.05 V205 .nHzO

 

(PVP)3,0V205.nHzO

250G
l

3400G

Figure 3.9. Electron paramagnetic resonance of irradiated samples.
(irradiation time : 12 h)

X "1(mole/emu)

116

 

3.0 103 E

Fresh sample

 

 

Inadiated sample
III'IIIIIIIIIrIIITIIIIIIIIIT
50 100 150 200 250 300
Temperature (K)

Figure 3.10. Variable temperature magnetic susceptibility
0f (PVP)1_0V205-nH20.

 

117

Table 3.1. Magnetic Data of Irradiated (Polymer)xV205-nHzO

 

X(TIP) d-spacing
Polymer x Heff (BM) (emu/ mole) contraction (A)
PVP 0.5 0.84 2.3x10’4 ~0
PVP 3.0 0.71 2.0x10‘4 2.1
Methyl-eel lulose 0.05 0.60 4.0x10'5 0.7
Methyl-cellulose 0.35 0.9 4.1 x10'5 1.7
PPG 0.5 0.8 1.4x10'4 0.6

 

118

BM, in the un-irradiated samples, to ~0.7-0.8 BM after 12 h irradiation and
the value is independent of the polymer type and its loading. The 0.7-0.8
BM corresponds to ~10% of V4+ centers in the framework, suggesting that
less than 5% of the polymer chains are oxidized. This small amount of
polymer oxidation is consistent with the unchanged infrared spectra of the
irradiated materials. Under the same irradiation conditions, no changes are
seen in the pristine V205-nHzO.

The irradiated materials also contain a new very broad electronic
absorption band centered at 1400 nm which increases in intensity as the
irradiation proceeds and is due to an intervalence transition associated with
the V4+ to V5+ centers14 as shown in Figure 3.11. The appearance of this
absorption band is consistent with the increase of V4+ concentration in the
vanadium oxide framework and further confirms the electron transfer from
the polymer to the V205 framework. The X-ray diffraction patterns of
irradiated compounds still show strong (001) reflections but the interlayer
distance is decreased somewhat. The magnitude of the contraction increases
with polymer loading, see Table 3.1. For example, in the case of (methyl-
cellulose)szOs compounds, the contraction is 0.7 A at x = 0.05 and 1.7 A at
x = 0.35. This may be due to the expulsion of a small amount of water from
the material upon reduction of V205 framework and possible
conformational changes in the oxidized polymer. The irradiated compounds

show diminished solubility in water.

3.3.3. Charge Transport Properties
Generally, the irradiated samples show a small but significant increase

in electrical conductivity. Variable temperature conductivity and

119

 

(b) T

Absorbance

(a)

 

 

 

T I I I I 1 ‘I I T I I I I I I

200 775 1350 1925 2500
nm

Figure 3.11. Absorption spectra of (PVP)1.0V205.nH20 (diffuse
reflectance mode) : (a) unirradiated fihn, (b) irradiated film (12 h).
The arrows at 1920 nm and 1440 nm indicate absorptions from water.

120

thermoelectric power plots of the fresh and irradiated (methyl-
cellulose)0,35V205.nHzO are shown in Figure 3.12 and Figure 3.13,
respectively. The temperature dependence of conductivity suggests
semiconducting character. The activation energy of both un-irradiated and
irradiated samples calculated from these data is similar at 0.24 eV indicating
only minimal structural changes in the V205 framework. As expected, the
Seebeck coefficients are negative and decrease with temperature, similar to
those in the PEO/V205 system. This confirms that these materials are
typical small polaron conductors15 where charge transport is through the
vanadium oxide framework. Upon irradiation, the Seebeck coefficient
increases dramatically due to the increase of electron carriers. Similar
results were obtained from the other materials as summarized in Table 3.2.
(PVP)3_0V205.nHzO has the lowest conductivity of 109 S/cm at room
temperature. The irradiated (PVP)3_0V205-nHzO shows a nearly 4 orders of
magnitude increase in conductivity. In general, compounds with low
polymer loading show a higher conductivity than those with high polymer
loading. A typical example is shown for the (methyl-cellulose)xV205.nHzO
system (for two different x values) in Figure 3.14. the lower conductivities
result from the "dilution" of V205 layers achieved by intercalated,
insulating, polymers which hinder the electrical contact between the
conducting V205 layers. Therefore, the electrical conductivity drops as the

intercalated polymer loading increases. Similar behavior was observed in
PEO/VzOs-system.

121

 

   

Log 0 (S/cm)
it <35 <31 is
' ' ['1 l | I I I l“l‘[’t"l l“1“1‘“ -

do
0

I
(D

:2;
l
l

 

s 6 7 8
1000/Temperature (1 /K)

0.)
.h

Figure 3.12. Four-probe variable temperature electrical conductivity
for films of (a) unirradiated (methyl-cellulose)o,35V205.nH20 and (b)

irradiated (methyl-cellulose)o,35V205.111120.

122

 

 

 

 

 

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A C (b)
{-750
> L
a l
a. i
r00
53-1500
CL 7
0' r
E :-
0) t
£2253:-
.
-300I...11.........1...111.14

200 225 250 275 300 325
Temperature (K)

Figure 3.13. Variable temperature thermoelectric power data for films
of (a)un-in'adiated (methyl-cellulose)o,35V205.uH20 and (b) irradiated
(methyl-cellulose)o,35V205.nHzO.

.030000200.0A0m0_0=00._>_=0=: 30 .000 930.003?0.280.230.15050
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125

3.4. Conclusion

In summary, we have produced a series of new intercalation
compounds of V205-nHzO with saturated water-soluble polymers. The
properties of the new materials are similar but not identical to those of the
previous PEO/V205 system. For example, although all of them are light
sensitive, the sensitivity decreases from PPG through PEO and methyl-
cellulose to PVP. Although the polymer intercalation always changes the
physical properties of the V205 host, the polymer/V205 films become
flexible with PEO and methyl—cellulose but brittle with PPG and PVP. The
results reported here warrant further studies on these and other polymers as
well as mixed polymers systems, with which we hope to produce a series of
inclusion compounds with controlled mechanical properties, light sensitivity

and electrical conductivity.

LIST OF REFERENCES

(1)

(2)

(3)

(4)

126

LIST OF REFERENCES

(a) Inoue H.; Yoneyama, H. J. Electroanal. Chem. 1987, 233, 291-295.
(b) Enzel P.; Bein, T J. Phys. Chem. 1989, 93, 6270-6272. (c) Okada,
A.; Kawasumi, M.; Usuki, A.; Kojima, Y.; Kurauchi, T.; Kamigaito, 0.
Mat. Res. Soc. Symp. Proc. 1989, 1_7_l_, 45. (d) Pillion, J .E.; Thompson,
M.E. Chem. Mater. 1991, 3, 777-779. (e) Enzel, P.; Bein, T. Chem.
Mater. 1992, 4, 819-824.

(a) Kanatzidis, M.G.; Tonge, L.M.; Marks, T.J.; Marcy, H.O.;
Kannewurf, C.R. J. Am. Chem. Soc. 1987, 109, 3797-3799. (b) Wu, C.-
G.; Kanatzidis, M.G.; Marcy, H.O.; DeGroot, D.C.; Kannewurf, C.R.
Polym. Mat. Sci. Eng. 1989, _6_1, 969-973. (c) Kanatzidis, M.G.; Wu, C.-
G.; Marcy, H.O.; DeGroot, D.C.; Kannewurf, C.R. Chem. Mater. 1990,
2(3), 222-224. ((1) Wu, C.-G.; Marcy, H.O.; DeGroot, D.C.; Schindler,
J.L.; Kannewurf, C.R.; Leung, W.-Y.; Benz, M.; LeGoff, E.;
Kanatzidis, M.G. Synth. Met. 1991, 4B3, 797-803. (e) Wu, C.-G.;
Marcy, H.O.; DeGroot, D.C.; Schindler, J.L.; Kannewurf, C.R.;
Kanatzidis, M.G. Synth. Met. 1991, 4_1_-4__3, 693-698.

 

(a) Ruiz-Hitzky, E.; Aranda, P. Adv. Mater. 1990, 2, 545-547. (b)

Lagadic, 1.; Leaustic, A.; Clement, R. J. Chem. Soc. Chem. Commun.
1992, 1396-1397.

(a) Giannelis, E.P. in press " Materials Chemistry .' An Emerging
Subdiscipline". (b) Yano, K.; Usuki, A.; Okada, A.; Kurauchi, T.;

(5)

(6)

(7)

(8)

(9)

127

Kamigaito, O. Polymer Preprints, 1991, 32, #1, 65. (c) Okada, A.;
Fukumori, K.; Usuki, A.; Kojima, Y.; Kurauchi, T.; Kamigaito, O.
Polymer Preprints, 1991, 32, #3, 540.

(a) Legendre, J.J.; Livage, J. J. Colloid Interface Sci. 1983, _94, 84—89.
(b) Aldebert, P.; Haesslin, H.W.; Baffier, N.; Livage, J. J. Colloid
Interface Sci. 1984, 23, 478-483. (c) Kittaka, 8.; Sasaki, S.; Ogawa, N.;
Uchida, N. J. Solid State Chem. 1988, 26, 40-51. ((1) Kamiyama, T.;
Suzuki, K. J. Non-Cryst. Solids 1988, 1%, 466-470. (e) Baffier N.;
Aldebert, P.; Livage, J.; Haesslin, H.W. J. Colloid Interface Sci. 1991,
141, 467-474. (I) Livage, J. Chem. Mater. 1991, 3, 578-593.

Liu, Y.-J.; DeGroot, D.C.; Schindler, J.L.; Kannewurf, C.R.;
Kanatzidis, M.G. Chem. Mater. 1991, 3, 992-994.

(a) Molyneux, P. in Water-Soluble Synthetic Polymers ; CRC press,
Inc.: New York, 1983 Vols. 1, 2. (b) Ott, E.; Spurlin, M. in High
Polymers; lnterscience Publishers, Inc. : New York, 1954 Vol. 5.

(a) Oster, G.; Immergut, E.H. J. Am. Chem. Soc. 1954, 26, 1393-1396.
(b) Rothschild, W.G. J. Am. Chem. Soc. 1972, 9_4, 8676-8683.

Aldebert, P.; Baffler, N.; Gharbi, N.; Livage, J. Mater. Res. Bull. 1981,
16, 669-676.

(10) Abello, L.; Husson, E.; Repelin, Y.; Lucazeau, G. J. Solid State Chem.

1985, 56, 379-389.

128

(11) Lemerle, J.; Nejem, L.; Lefebvre, J. J. Inorg. Nucl. Chem. 1980, 42,
17-20.

(12) Baiker A.; Dollenmeier, P.; Glinski, M.; Reller, A.; Sharma, V.K. J.
Catal. 1988, 111, 273-285.

(13) (a) Boudreaux, X.A.; Mulay, L.N. "Theory and Applications of
Molecular Paramagnetism", John Wiley and Sons: New York 1976. (b)
Drago, R.S. "Physical Methods in Chemistry" W.B. Sanders Co.:
Philadelphia, 197 7 .

(l4) Babonneau, F.; Barboux, P.; Josien, E.A.; Livage, J. J. Chim.
Physique 1985, 32, 761-766.

(15) Bullot, J.; Cordier, P.; Gallais, O.; Gauthier, M.;Livage, J. J. Non-
’ Cryst. Solids 1984,63, 135-146.

CHAPTER IV
STABILIZATION OF ANILINIUM IN VANADIUM(V)

OXIDE XEROGEL AND ITS POST-INTERCALATIVE
POLYMERIZATION TO POLY(ANILINE) IN AIR

129

130

ABSTRACT

The oxygen-induced polymerization of anilinium to polyaniline in
the layered compound (C6H5NH3)0,4V205.0.4H20 to form {l/n(-C6H4NH-
)n}o,4V205.0.4H20 is reported. (C6H5NH3)0_4V205.0.4H20 was prepared
by the reaction of V205 xerogel with C6H5NH3I in CH2C12 for two days.
X-ray diffraction and infrared spectroscopy confirmed anilinium inside the
layers of V205. Exposure to air resulted in an intra-lamellar
polymerization of anilinium to polyaniline. Infrared spectroscopic data
show the formation of emeraldine salt of polyaniline. The interlayer
expansion (5.6 A) is consistent with a monolayer of polymer chains in
V205 framework. The oxygen-induced polymerization is activated by
vanadium oxide. Magnetic susceptibility measurements and electron
paramagnetic resonance spectroscopy indicate that the V205 framework
loses electron during the polymerization process. The electrical
conductivity of {1/n(-C6H4NH-)n}0,4V205.0.4H20 is two orders of
magnitude higher than that of its precursor (10‘5 S/cm) while the
thermopower of the former is smaller (-20 uV/K). The MW of the
polyaniline formed in the intralamellar space was estimated by gel

permeation chromatography.

131

4.1. Introduction

During the last few years we have investigated in detail the redox
intercalative polymerization of several organic molecules such as aniline,
pyrrole and 2,2'-bithiophene in vanadium oxide xerogel.1 The products
contain the corresponding conjugated polymers poly(aniline) (PANI),
poly(pyrrole) and poly(thiophene) within an electrically conductive mixed-
valence V4+N5+ lamellar host. Redox intercalation2 alters the band
structure of vanadium oxide forming bronze-like electrically conductive
materials.3 The formation of PANI from anilinium and vanadium oxide
gels is relatively fast and the study of this heterogeneous reaction is
difficult. It is presumed that the first step in the insertion of PANI is
intercalation of the monomer in V205 framework. One way to follow the
oxidation of aniline by the vanadium oxide would be to trap anilinium
between the layers of the host and then observe its conversion to
polyaniline (PANI) upon oxidation. The challenge is to prevent anilinium
from being oxidized by V205.nHzO before controlled polymerization can
be initiated. We accomplished this by satisfying the oxidative power of
V205.nHzO with electrons from a different source such as iodide. In this
chapter, we report the successful insertion of intact anilinium molecules in
V205.nHzO and their intra-lamellar conversion to PANI upon exposure to

ambient oxygen.

4.2. Experimental

Materials

132

NaVO3, NaOH, acetone, methylene chloride, and anilinium iodide
were purchased from commercial sources and were used without further

purification.

Physicochemical Methods

See chapter two.

Preparation of V205-nH20 Xerogel

See chapter two.

Preparation of (C6H5NH3)0,4V205-0.4H20

Under a nitrogen atmosphere, powdered 0.5 g (2.37 mmol) of
V205.1.8H20 reacted with 2.1 g (9.48 mmol) of anilinium iodide in 50 ml
of methylene chloride at room temperature. After stirring for two days,
the dark-blue product was isolated from filtration and washed with acetone.

The composition of the product obtained from thermogravimetric analysis
(TGA) under oxygen flow gave (C6H5NI-I3)o,4V205.0.4HzO.

Extraction of Polyaniline from (PANI)0,4V205.0.4H20
(PANI)0,4V205.0.4H20 was added to excess 2 wt% NaOH solution.

After one day of stirring at room temperature, the black precipitate was

collected by filtration, washed with water and acetone, and dried in air.

4.3. Results and Discussion

4.3.1. Synthesis and Characterization of

133

(C6H5NH3)0,4V205.0.4H20

The anilinium intercalated vanadium oxide gels is formed according
to eq (4.1)

X C6H5NH3+F + V205-nH20 ————>
(C6H5NH3)XV205'IIH20 + (II/2)12 (4.1)

The V205 xerogel oxidizes iodide, which is a better reducing agent than
anilinium, to iodine. The anilinium is intercalated into the reduced
framework to neutralize the negative charges on the layers. The
intercalation is confirmed by the net increase of ca. 5.1 A in the interlayer
distance as shown in Figure 4.1(A). The very broad (001) diffraction peak
corresponds to a very short coherence length, perpendicular to the layers
stacking axis, which is estimated to be 25A by using Scherrer formula.
This is considerably smaller than the 100A found in V205 xerogel itself
and indicates considerable disruption of the stacking order of the vanadium
oxide layers upon intercalation. The presence of anilinium is

unambiguously established by infrared spectroscopy as shown in Figure
4.2(A).

4.3.2.Polymerization of (C6H5NH3)0,4V205.0.4H20

Exposure to air induced profound changes in the infrared spectrum
of the material, shown in Figure 4.2(B) where the anilinium vibration
pattern gradually disappeared and the strong characteristic pattern of the
emeraldine salt form of polyaniline became evident.4 The changes of the

position and shape of the stretching vibration peaks of the vanadium oxide

I34

 

(oor)
/
3‘
'3'
B
3
E
(001)
k /

 

 

 

 

5. IO. 15. 20. 25. 30. 35. 40. 45. 50.

2 6 ( Degrees)

(A)

(B)

 

Figure 4.1 X-ray diffraction patterns from (A) (C5H5NH3)0,4V205.0.4H20

and (B) {l/n(-C6H4NH-)n}o.4V205.0.4H20.

55. 60.

135

 

 

 

TRANSMI‘I'I'ANCE

(B)

 

 

‘ /

are

 

 

zéaozworiaorhoréoormoam o
WAVENUMBER

Figure 4.2 Infrared spectra (KBr pellet) of (A) (C6H5NH3)0,4V205.0.4H20
and (B) {l/n(-C6H4NI-I-)n}o,4V205.0.4H20. *peaks are from anilinium ion.

136

framework are also significant. The V=0 vibration peak changes from 990
cm'1 to 1000 cm"1 and the V-O-V vibration peaks5 shift from 852 cm"1 and
530 cm“1 to 750 cm‘1 and 496 cm‘l. This spectroscopic difference is due
to the greater degree of reduction in (C6H5NH3)0,4V205.0.4H20 1 than in
{1/n(-C6H4NH-)n}0,4V2O§.0.4HzO 2. This is confirmed by magnetic
susceptibility measurements presented below. The infrared absorption
peaks of 2 are similar to those of (PANI)xV205.nHzOlar6 3, prepared
directly from aniline and V205.nHzO, as shown in Table 4.1. After
digestion of the V205 framework, the absorptions of the extracted PANI
from 2 occur at slightly higher energies than bulk PANI. This suggests
that the extracted PANI has lower molecular weight, see below. The (001)
peak in the X-ray diffraction pattern, shown in Figure 4.2(B), of the
oxidized product 2 narrows dramatically compared to that of 1 and reveals
a small 0.5 A interlayer expansion. This indicates that the polymerization
is intra-lamellar, forming a monolayer of polyaniline chains inside the
framework. The conversion is complete in three to four weeks, judged
from infrared spectroscopy. The estimated coherence length along the
layers stacking axis increases threefold to ca. 90 A, suggesting a
significantly improved lattice organization. Compared to 3, the compound
2 shows additional 0.5 A expansion. The overall reaction is represented in
Scheme 4.1.

The mechanism of this unprecedented post-intercalative oxidative
polymerization is complicated but it must be related to the ability of
vanadium centers7 to activate oxygen. Simple anilinium salts are not
oxidized to polyaniline under the experimental conditions employed here.
Therefore, the vanadium oxide must be implicated. This is consistent with

the ability of vanadium oxide to catalyze oxidation of organic molecules.

137

.o 000000.000 800.0. .3000.

 

 

N 8000
Now 002 omfl .82 SE .32 Hz<m 00000.00m
3... 8: 9.2 .800 SE .002 0,20 030
000 .5 .80 a: as .002 E: .82 .. 0 88980
0% .000 .82 mm: 2.2 .32 me: .002 a 28088
9-83 3-83 9-83 $-83 3-83
020308000 mOm> 8003.00-38 $020-03 M00305 Z-U 0.03305

05008 0-0 0528 0-0 a 0228 0-0 0&0 0-0

 

025 022.000
eee 020.0 0:00 .0 00020090030 .0 005000910030 00 meweem SEES 0: .3. 0300.

138

 

V205
NH3 NH3
V205
Oxygen

 

M”?

V205

 

+

H20 01' H202

Scheme 4.1.

139

One role for the V205 framework could be as an electron relay between
the reducing guest and oxygen. This is supported by the magnetic
susceptibility data of l and 2 as shown in Figure 4.3 where 2 shows
smaller magnetic susceptibility than 1. This indicates few unpaired
electrons in 2. Both compounds are paramagnetic exhibiting Curie-Wiess
behavior with a contribution of temperature-independent van Vleck

paramagnetism (TIP)8 as represented in eq (4.2).
X(measured) = x(Curie-Weiss) + NW) (42)

The TIP term is due to the interaction of the ground state and the excited
states in an applied magnetic field and is discussed in chapter five. The
X(T1p) and ueff for 1 and 2 are summarized in Table 4.2. Compound 1 has
significantly higher ueff than 2 indicating fewer V4+(d1) centers in 2.
These data suggest that oxygen removes electrons from the vanadium oxide

framework, which in turn removes electrons from anilinium.

Table 4.2. X(T1p) and ueff Values for (C6H5NH3)0,4V205.O.4H20 and
{1/n(—C6H4NH-)n}0,4V205.O.4H20.

 

Ueff* me)

Material (BM) (emu/mole)
(C6H5NH3)0.4V205-0.4H20 1 .30 3.4e-4
{ 1/n('C6H4NH')n}0.4V205-0-4H20 0.87 6.5e-5

 

*Calculated from X(Curie-Weiss)-

140

 

 

 

 

3000 .
'l
2500‘:
{3 fl { 1/n(-C6H4NH-)n}O.4V205-0-4H20
E 2000':
d) .
\ .
.2 l
O 1500‘1
8 i
v -l
"'" “l
I —
X 1000
500‘
j (C6H5NH3)0.4V205.0.4H20
01"'1""I""I"'rl"*Tl'*'*
0 50 100 150 200 250 300
Temperature (K)

Figure 4.3. Variable temperature magnetic susceptibility of
(C6H5NH3)0.4V205.0.4H20 and {1In(-C6H4NH-)n}0.4V205.0.4H20

141

4.3.3. Electron Paramagnetic Resonance (EPR)

The room temperature EPR spectra of (C6H5NH3)0_4V205.0.4H20 1
and {1/n(-C6H4NH-)n}0_4V205.0.4H20 2 show symmetric broad signals
centered at g ~ 1.96 as illustrated in Figure 4.4. The relatively broad
signals derive from the reduced vanadium oxide framework where the V4+
centers experience magnetic exchange interactions.9 The sharp EPR
resonance (< 20 G) arising from the polarons of PANI10 is not observed in
2, suggesting that magnetic coupling between the PANI and the reduced
framework is significant6. The peak width (Apr) is 660 G and 130 G for
l and 2, respectively. The larger Apr in 1 (increased magnetic exchange
broadening) is consistent with larger V4+ concentration in this compound
compared to 2 and is in agreement with the magnetic susceptibility data for

these materials.

4.3.4. Thermogravimetric Analysis (TGA)

TGA diagrams of 1 and 2 under nitrogen flow are shown in Figure
4.5. Both samples lose weight continuously from ~100°C to 900°C. This is
due to oxidative degradation of anilinium and PANI by the vanadium oxide
framework. Interestingly, I shows slightly better thermal stability than 2,
even though 2 contains PAN and is expected to be more stable. This may
be because in 2 there are more V5+ centers than in l, which help to
oxidatively degrade PANI. This phenomenon was also observed at fresh
and aged (PANl)xV205.nH20 (formed directly from aniline) where fresh

samples are more stable than aged samples due to the same reason.

142

(a)

 

 

(b)

 

 

 

236-6

34000

Figure 4.4. Room temperature EPR spectra of (a) (Csl-ISNH3)0.4V205.0.4H20
and (b) {l/n(-C6H4NH-)n}o.4V205.0.4H20

143

 

Weight %

 

 

 

 

65 l l l I l I l I r I
O 200 400 600 800 1000

Temperature (0C)

T I I

Figure 4.5 TGA diagrams or (a) (C6H5NH3)0.4V205.HH20 and
(b) {1,n(-C6H5NH-)n}0.4V205J’1H20
(Samples have been dried under vaccum prior to use)

144

4.3.5. Molecular Weight Studies

The PANI isolated from 2 is soluble in N-methylpyrrolidinone
(NMP) and molecular mass studies using gel permeation chromatography
(GPC) were carried simultaneously with similar studies on bulk chemically
prepared PANI. The GPC traces reveal a broad monomodal molecular
mass distribution, see Figure 4.6, with a peak maximum corresponding to
ca. 14,000, compared with 32,000 found for bulk PANI“, see Table 4.3.
By comparison, a molecular mass of 27,000 is obtained from PANI
extracted from 3. The considerably smaller molecular mass of the
polymer in 2 is rationalized by the fact that its formation occurred in a
structurally constrained environment, in the solid state, in which the

polymerization kinetics are slow.

Table 4.3. Molecular Weights of Bulk and Extracted Poly(aniline)

 

Material Mp Mn Mw

Bulk PAN 1 32,000 7,700 69,000
Extracted PANI from 2 14,000 12,300 19,800
Extracted PANI from 3 27,000 17,700 44,500

 

Mn (number-average molecular weight) = (XiNiMD/(XiNi).
Mw (weight-average molecular weight) = (ZiNiMi2)/(ZiNiMi).

Mp : molecular weight at the maximal absorption position.

4.3.6. Charge Transport Properties
Variable-temperature electrical conductivity of 1 and 2 are shown in

Figure 4.7. Compound 2 shows enhanced electrical conductivity consistent

145

(a)

(b)

 

 

 

\ A J‘
r r 1
30 60

Retention time (min)

Figure 4.6. GPC diagrams of (a) bulk polyaniline and (b) extracted
polyaniline from {lln(-C6H4NH-)n}0,4V205.0.4H20.

146

 

V'VV

  

a
.L
1

l l/n(-thNH-)n}o.4V2050.4flzo

U111 'WTTU I I

Log 0 (S/cm)
4:
0

do
'r'VYTlVUV

0 (“Ma’hdlesOAHzO

 

T'UTIV'U' "'

 

.11...-i.r..1a.n.r....lrz.rp,__._‘_l,
50 100 1 50 200 250 300 350

Temperature (K)

Figure 4.7. Four-probe pressed pellet variable temperature electrical
conductivity data of (C6115NH3)0,4V205.0.4H20 and {1In(-C6H4NH-

)n}o,4V205.0.4H20.

147

with the presence of PAN]. However, the conductivity is approximately
two orders of magnitude smaller than that of 3. This may be due to the
smaller chain length of PANI in 2 compared with 3, described below. The
different electrical properties of 1 and 2 are emphasized in the
thermoelectric power measurements, see Figure 4.8. At 300K the
compound 1 shows a small negative Seebeck coefficient of -15 to ~20
uV/K, while 2 exhibits a large negative Seebeck coefficient of ~90 to —1 10
uV/K. The more negative coefficient of 2 is consistent with the fewer
charge carriers in the vanadium oxide framework compared with those of
1, as suggested by the magnetic susceptibility. However, this is inconsistent
with the higher conductivity of 2. The thermally activated temperature
dependence of conductivity and the negative Seebeck coefficient suggest n—
type semiconducting character for both materials.12 From these results we
conclude that in 2, despite the presence of PANI, the charge transport
properties are dominated by the vanadium oxide. The role of PANI in
assisting charge transport is probably significant since, the material shows
higher conductivity than 1, but it contains fewer carriers in the vanadium

oxide framework.
4.4. Conclusion

The topotactic oxidative polymerization of intercalated anilinium in
vanadium oxide xerogel is unprecedented. The reaction itself carriers
important implications for studying potentially regioselective intra-lamellar
coupling reactions and for the future inclusion synthesis of conjugated
polymers in a broad class of layered materials by solid-state polymerization

of their corresponding monomer intercalated precursors.

148

 

 

 

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.- OmOCBDM
g ,.
S _ (“£51013 ’thzOs-OAl‘ho
£5 -50_-
El .
3
8. .
3 ' o
__ .100 _. W
a . MW 3"“ °
1- .

{ l/n(-CMH~).}0,4vzoso.4nzo
.150 r . . r l . r . r 1 . . . . l r r r r

 

1 50 200 250 300 350
Temperature (K)

Figure 4.8. Variable-temperature thermoelectric power data of
(CoflsNH3)o,4V205.0.4H20 and {lln(-C6H4NH-)n}0,4V205.0.4H20.

LIST OF REFERENCES

149

LIST OF REFERENCES

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(3)

(4)

(5)

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(7)

(8)

(9)

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Glatkowski, P.J.; Cajipe, V.B.; Fischer, J.E.; Cromack, K.R.;
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Cryst. Solids 1984,6_8, 135-146.

CHAPTER V

INVESTIGATION OF THE VANADIUM OXIDE XEROGEL
BRONZES: AszOsonflzO (A = K AND Cs)

152

153

ABSTRACT

The synthesis of bronze-like AszOs-nHzO xerogels (A = K and Cs,
0.05 < x < 0.6) and studies of their chemical, physical and charge transport
properties as a function of x are reported. The reduced V205 xerogels
were prepared by the reaction of the xerogel with various amounts of
alkali iodide (K1 and C31) in acetone under N2 atmosphere for three days.
X-ray diffraction and spectroscopic data indicate that the V205 framework
in AszOs-nHzO maintains the pristine V205 xerogel structure. The
increased V4+ ((11) concentration in the V205 framework causes the
disappearance of EPR hyperfine structure and the increase of magnetic
susceptibility and electrical conductivity. The magnetic behavior is best
described as Curie—Weiss type coupled with temperature independent
paramagnetism (TIP). The Curie constant and EPR peak-width of the
AszOs-nHzO materials show a maximum value at x ~ 0.3, suggesting
antiferromagnetic coupling of V4+ centers as their population increases.
Electrical conductivity slightly increases with V4+ concentration, and its
temperature dependence indicates a thermally activated process. The
thermoelectric power of the AszOs-nHzO materials is negative and
becomes less negative with increasing V4+ concentration. Optical diffuse

reflectance spectra are reported.

154

5.1. Introduction

Recently, it was shown by our group that the redox intercalation of
organic monomers such as aniline, pyrrole and 2,2'-bithiophene yields
layered materials containing monolayers of conductive polymers in the
intralamellar space of V205 xerogell. The vanadium oxide network and
ambient oxygen are reduced to form V4+ centers while organic monomers
are oxidatively polymerized into electrically conductive polymers. This
results in new molecular composites of two electrically active but
chemically diverse components: organic conductive polymers and inorganic
vanadium bronzes. In order to achieve a better understanding of the role
of the conductive polymer inside the oxide sheets, it is important to
understand the nature and properties of the reduced V205 framework
alone. Of course, numerous studies have been published on crystalline
bronze phases of the type AszOs2 but in these materials the V205
structure is different from that of V205 xerogels and it varies as a function
of A and x. Therefore, these materials are not representative of the
reduced xerogel. To our knowledge, complete and systematic studies of
compounds with a reduced V205 xerogel framework are rare.3
Therefore, a series of reduced V205 xerogels were prepared by the
reaction of the xerogel with various amounts of alkali iodide (KI and CsI).
The intercalants are closed-shell K+ and Cs+ ions which can be considered
as "innocent" species (e.g. diamagnetic and insulating), thus, allowing the
properties of the reduced V205 framework to be studied with no

interference from the guests.

155

In this paper, we report the synthesis of the reduced bronze-like

V205 xerogels as well as their optical, magnetic and charge transport

properties as a function x (i.e. V4+ concentration).

5.2. Experimental Section

5.2.1. Materials

Sodium metavanadate (NaVO3), potassium iodide (KI), cesium iodide
(Csl) were purchased from Aldrich Co., Milwaukee, WI and were used
without further purification. Elemental analyses were done by Galbraith

Laboratories, Knoxville, TN and Oneida Research Services, Inc.,
Whitesboro, NY.

5.2.2. Measurements

Infrared spectra were recorded from 4000 to 400 cm-l with a
resolution of 1 cm'1 on a Nicolet 740 FT -IR spectrometer. Samples were
recorded in a pressed KBr matrix under N2 flow. IR diffuse reflectance
spectra were also recorded on the same instrument equipped with a
reflectance attachment purchased from Spectra. Tech. Inc. Samples were
pressed into pellets and directly put on a sample holder. A gold mirror
was used as the reference.

The instruments and experimental setups for X-ray diffraction, EPR,
magnetic susceptibility, UVN is, electrical conductivity and thermopower
are the same as those in chapter 2.

Quantitative elemental analysis was done by the SEM/EDS (Scanning
Electron Microscopy/Energy Dispersive Spectroscopy) technique on a
JEOL JSM-35C microscope equipped with a Tracor Northern TN 55000

156

X-ray microanalysis attachment. Samples were glued on an aluminum stub
with conductive carbon paint for the dissipation of accumulated charges.
Typical experiment conditions are as followed: accelerating voltage, 20
KeV; detector window, beryllium; take-off angle, 27 deg.; accumulation
time, 60 sec. A standardless quantitative analysis solfware program was
used to analyze the characteristic X-ray peaks of the elements present in the
sample. Correction factors for KN and Cs/V ratios were determined from
known compounds such as KVO3 and CsVO3. The alkali-to-vanadium
ratio for each sample obtained by averaging three independent
measurements.

The calculation of one-dimensional (l-D) electron density maps was
based on the X-ray reflection data using the observed (001) group of
reflections. Eight reflections were used for Cso_27V205-nHzO out to (1003
= 1.37A. The intensities were obtained from the integrated peak areas.
The structure factors of these reflections were derived from their
intensities and corrected for Lorentz-polarization effects. The signs of the
phases for the structure factor calculation were directly obtained from the
scattering contributions of the V205 framework alone. The signs of the
phases were also checked by recalculation including the contribution of the
Cs+ ions. All but one reflection changed sign but this did not substantially
change the electron density pattern. The calculated and observed structure

factors of Cso,27V205-nHzO are shown in Table 5.1.

5.2.3. Preparation of V205 Xerogel

See chapter two

5.2.4. Preparation of AxV205~nH20

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Powdered V205 xerogel (0.5 g, 3.38 mmol) was added to a 50 ml of
acetone with a stoichiometric amount of KI or Csl. The KINzOs and
CsI/V205 molar ratios were varied from 0.1 to 1.0 in increments of 0.1.
The reaction was stirred under N2 atmosphere for three days. The dark
product was filtered, washed with acetonitrile and then dried under
vacuum. The compositions of AszOs-nHzO compounds were determined
from Elemental analysis and SEM/EDS. An attempt to produce the
AxV205-nH20 materials with x > 0.6 failed, because over-reduction caused
amorphization of the V205 framework. The materials used to calculate the
1-D electron density map were prepared using films of V205-1.8H20
xerogel. The n is ~].l when x < 0.1 and ~ 0.5-0.6 when x > 0.1.

5.3. Results and Discussion

5.3.1. Structure of V205 Xerogel

The structure of the V205-nH20 xerogel is not accurately known but
two motifs have been proposed. Livage and coworkers suggested a layered
structure composed of a single corrugated slab of V205 with a corrugation
step of 2.8 K4 The layers between the steps have the same structure as
crystalline V205. Oka and coworkers support a bilayer model with flat
V205 slabs based on the structure of NaxV205.5 These models are shown
in Figure 5.]. They mostly satisfy the observed X—ray diffraction data in
the reflection mode (001 reflections), although a poor agreement is
observed with X-ray diffraction data in the transmission mode. However,
based on the observed density of V205-nH20 xerogel which is ~ 2.5 g/cm3,
Oka's model appears to be most consistent (dcajcd ~ 2.87 g/cm3). The
Livage model gives a dcalcd ~ 1.5 g cm3. The density of AszOs-nHzo

159

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ranges between 2.7 and 3.3 g/cm3. Therefore, we prefer to use Oka's
model. Incidentally, similar calculations based on Livage's model do

substantially change the resulting conclusions

5.3.2. Synthesis and Spectroscopy~
The reduced V205 xerogels were produced according to eq(5.l).

y Al + V205.nH20 —> AyVZOS'nHZO + (Y/Z) I2 (51)

A=K,Cs

The V205 xerogel oxidizes iodide to iodine and the alkali ions are
intercalated into the reduced framework to achieve electroneutrality. The
composition, interlayer distance, and infrared spectroscopic data for
KszOs-nHzo and CsxV205-nl-l20 compounds are summarized in Table
5.2 and Table 5.3, respectively. The AXVZOS-nHzO compounds are brown
or green when x < 0.1 and turn blue when x 2 0.1. The hydrated water, n,
decreases with the rise of x from 1.8 when x = 0 (V205 xerogel) to ~ 0.6
when x ~ 0.1 and becomes constant when x > 0.1. Generally, the infrared

spectra of the reduced compounds show three characteristic vibration bands

from the V205 framework below 1100 cm-1. A typical infrared spectrum
from Ko,33V205-nH20 is shown in Figure 5.2. The band at ~ 1000 cm-1 is
assigned to the V=O vibration and the bands at ~750 cm’1 and ~500 cm'1
are attributed to the in-plane and out-of-plane V-O-V vibrations,6
respectively. The presence of the three bands suggests that the reduced
V205 framework is intact. The V=O vibration generally shifts to lower
energy as the increase of alkali ion concentration increases, see Figure 5.3.

The red shift is due to the addition of electrons into antibonding d orbitals

161

Table 5.2. Summary of Composition, Color, Interlayer Spacing and
Infrared Data for KszOsonHzO

 

d-spacing Vibration bands
Formula Color (A) (cm‘ ])
V205-1.8H20 red 11.55 1015, 760, 510
K0,03V205.l.1H20 green 11.65 1012, 759, 51.3
K0,26V205'nH20 dark blue 10.28 999, 762, 527
Ko_33V205-nH20 dark blue 10.10 996, 766, 537
K0_39V205-nH20 dark blue 10.05 994,760, 522
Ko,44V205-nH20 dark blue 9.87 996, 774, 547
Ko,47V205-n}-I20 dark blue 9.86 996, 761, 530
K055V205-nH20 dark blue 9.72 984, 759, 527

 

l) n is in the range of 0.5~0.6.

162

Table 5.3. Summary of Composition, Color, Interlayer Spacing and
Infrared Data for CsszOsonlle

 

 

d-spacing Vibration bands

Formula Color (.4) (cm' 1)
CsoszOslleO brown 11.65 1012, 756, 513
Cso_1gV205~nHzO dark blue 11.2 1010, 760, 520
C8026V205'IZH20 dark blue 10.8 1006, 762, 532
CsogszOs-nHZO dark blue 10.8 999,754, 535
Cso,35V205-nH20 dark blue 10.8 999, 755, 524
Cso,3gV205-nH20 dark blue 10.8 997, 762, 530
Cso,41V205'nH20 dark blue 10.7 994, 755, 523

 

1) n is in the range of 0.5~0.6.

163

 

 

 

 

 

E:
a f
8 H20
,5: 996
766
537
T I I I I T l T —l T l I I I l
4000 3100 2200 1300 400
Wavenumber

Figure 5.2. Infrared spectrum of K033V205 0.5H20 (KBr pellet).

A
93
v

Wavenumber

E

Wavenumber

164

 

1020 ,
1015—i
1010—é
1005-1
10004; ,

995? ,
990-3
985-§ .

930: ...,.H.W.”,fTfiirrfllnn
0 0.1 0.2 0.3 0.4 0.5 0.6

X
10201
1015

d
an

 

 

 

1010‘; o

.1
1005{

1000€

995%

 

 

 

990‘....,f...,-...r.-..l.,,,
0 0.1 0.2 0.3 0.4 0.5

Figure 5.3. Infrared spectra] shifts of V=O vibration energy as a
function of x : (a) KXVZOS-nHZO and (b) CsxVZOS-nHZO.

165

of vanadium, probably coupled with ionic interactions between the oxygen
of V=O and the alkali ions.

The optical absorption spectra of the AXV205-nH20 compounds
show a very broad band, centered around 1400 nm with a tail extending
into the infrared region (Figure 5.4). The band is described as an
intervalence transition from V4+ to V5+ centers.3 It is absent in pristine
V205 xerogel due to the very small number of V4+ centers. The
appearance of this intense intervalence band confirms that the V205

framework is reduced.

5.3.3. X-ray Diffraction

Figure 5.5 shows a typical X-ray diffraction pattern for the
AxV205-nH20 compounds in which (001) peaks dominate, indicating that
the layer structure is maintained. The interlayer spacing slightly decreases
from 11.65 A when x = 0.08, to 9.72 A when x = 0.55 in KXV205-nH20,
and from 11.65 A when x = 0.07 A, to 10.7 A-when x = 0.41 in
CsszOs-nHzo (Tables 5.2 & 5.3). The decrease in the interlayer height
with increasing x is due to the loss of intercalated water and the increased
ionic attractive interactions between the positively charged alkali ions and
the negatively charged V205 layers. For the same x, the CsxVZOs-nHzo
show a slightly higher expansion than the KszOs-nflzO, consistent with
the larger size of Cs”.

In order to determine the position of alkali ions in the V205
framework, we performed the 1-D electron density calculation along the
layer stacking direction (0 axis). Based on Oka's model, a projection of the
calculated electron density of Cso,27V205-0.5H20 is shown in Figure 5.6.
Clearly, the two strong peaks at z = 0.87 and 1.13 are observed with a

166

 

 

 

 

Absorbance

 

 

 

 

I l f l I I I r f I I

I
200 775 1350 1925 2500
nm

Figure 5.4. Optical absorption spectra of (a) V205 xerogel
and C8027V205°0.5H20.

I I I

167

 

 

 

 

 

 

 

 

 

 

 

 

 

(001)
(a)
(003)
.13: J (004) (005)
E) A A ,. -
E (001)
(003) (b)
J (002) (004) (005)
.,..r....,....,.”firmffinn
0 10 20 30 40 50 60

2 Theta

Figure 5.5. X-ray diffraction patterns of (a) V205 xerogel and
(b) C8027V205'0.5H20.

168

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169

separation of 2.8 A. They are readily assigned to the two V015 sheets.
The peak at z I: 0.73 shows a distance of 1.6 A with the most adjacent
V015 sheet, consistent with vanadyl groups perpendicular to the V015
sheet. This is consistent with the projection of a monolayer of the V205
structure along this axis. The peak at z = 0.5 is attributed to Cs+ ions,
residing in the middle of the interlayer gallery. Similar results are also
observed for the other AszOs-nHzo compounds with x < 0.3. However,
the electron density calculation for the AXV205-nH20 with x > 0.3 is
impossible due to lower crystallinity and insufficient numbers of

reflections.

5.3.4. Magnetic Susceptibility Studies

Magnetic susceptibility data as a function of temperature for several
AszOs-nHzO compounds are illustrated in Figure 5.7. The data when
plotted as 1/X vs T, show a slight curvature away from linear dependence,
thus deviating from Curie-Weiss law. However, a linear dependence is
obtained when a small constant correction is applied to the susceptibility,
see Figure 5.8. We interpret the magnetic behavior as Curie-Weiss type
with a small amount of deviations due to van Vleck temperature-
independent paramagnetism (T IP).7 Thus, the measured molar magnetic

susceptibility (an) can be expressed by eq (5.2).

Xm = X(Curie-Weiss) + X(TIP) (5.2)

C

X urie— eiss = _— (53)
(C w ) T-0

(m0u)le/em

-l

X

170

 

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3500? (a)
3000":
525001 (b)
2000"
V1500"
1oooj (C)

500E y“?

 

 

 

 

Temperature (K)

Figure 5.7. Inverse magnetic susceptibility as a function of
temperature for (a)Ko.03V205-nH20, (b)K026V205-nH20 and
K033V205°HH20-

0 50 100 150 200 250 300

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Temperature (K)

Figure 5.8. Inverse magnetic susceptibility as a function of temperature for
K026V205'nH20 3 (a) me), (b) X(Curie-Weiss) and (C) Xm-

172
Substituting eq (5.3) for X(Curie-Weiss) in eq (5.2) produces eq (5.4)

C
Xm= —— + XmP) (5.4)
T-B

where C = Ng262/4k is the Curie constant and 8 is the Weiss constant.
Fitting the measured magnetic susceptibility data with eq (5.4), the
resulting X(T[p), C and 6 for the AszOs-nHzO compounds were extracted
and are summarized in Tables 5.4 and 5.5. Depending on x, the “eff
calculated from X(Cufie-weiss) is in the range between 0.6 and 1.0 BM,
confirming the increased number of V4+ centers in the framework. For
comparison, pristine V205 xerogel has a “eff of ~ 0.3—0.4 BM because of
residual small amounts of V4+ impurities which unavoidably form during
preparation.

The small correction applied to the susceptibility data is attributed to
temperature independence paramagnetism. The TIP term originates from
the second-order Zeeman effect which describes the interaction of the
ground state and the excited states in an applied magnetic field. The value
is inversely proportional to the energy differences (AB = Ee-Eg) between
the ground and excited state7, see eq (5.5). Thus the X(T[p) to be

significant the AE must be very small.

 

<w leplux?2
X(T1P)=2Nf322 in, (5.5)

N is Avogadro's number, 6 is the Bohr magneton of the electron, mg and

we are wave functions of the ground and excited states respectively, and 6p

Table 5.4. Magnetic Susceptibility Data for KxV205-nH20 Compounds

173

 

 

Xm me) “eff“

x (emu/mole) (emu/mole) (spin only) C 0 (K)
0.08 2.67e-4 5.6i4.0e—5 0.723.007 0.06i0.01 -2i2
0.26 4.44e-4 l . 1:0.5e-4 0.89:0.06 0. li0.01 -3.7i4
0.33 5.30e-4 2.010.5e4 0.88i0.07 0.1 1:00] 6.75
0.39 4. l4e-4 l .4i0.4e—4 0.83i0.03 0.09i0.01 -6i4.6
0.47 3.98e-4 l .4i0.4e—4 0.78i0.06 0.08¢0.0l -7.8_+_4
0.55 4.32e-4 1.7i0.4e-4 0.78:0.06 00810.01 9.615

 

*Calculated from (Xm-me)).

l

174

Table 5.5. Magn_etic Susceptibility Data for CsxV205~nH20 Compounds

 

 

xm X(TIP) “eff,k

x (emu/mole) (emu/mole) (spin only) C 0 (K)
0.07 2.13e-4 4.9i2.0e-5 06210.04 0.05:0.01 0.65:3
0.18 3.83e-4 7.0i4.0e-5 086310.06 0.09i0.01 -l .6i3.4
0.26 4.97e-4 l.4i0.6e-4 0.89i0.05 0. l li0.02 3.915
0.28 5.75e—4 2.210.594 0.92:0.06 0. 10i0.01 5:15
0.35 5.20e-4 l.9i0.5e-4 0.88:0.06 0. 100:0.01 -5i4
0.38 5.14e-4 2.0i0.5e-4 0.86i0.07 0.09100] 6.6215
0.41 5.38e-4 2.4i0.5e-4 0.83210. 10 0.09:0.01 72:55

 

*Calculated from (Xm-Xa‘rpp.

175

is an unspecified operator. In this case the orbitals of interest are the V4+
d orbitals. Therefore, if the X(T[p) and the orbital ordering in the ground
state and excited states are known, AE can be calculated. In V205 xerogel,
the vanadium is assumed to be in a distorted square pyramidal geometry
with approximate sz symmetry.8 Thus, the idealized orbital diagram is
shown in Figure 5.9. Based on this scheme the energy difference between
the ground ((1 electron in dyz orbital) and excited (d electron in dxz orbital)
states is expected to be quite small. The ordering of dxz, dyz and dxy levels
depends on the extend of 7r acceptor character of dxz and dyz orbitals. In
the case of V205 framework the TI character of these orbitals is expected to
be substantial because of the filled pz orbitals of the bridging equatorial
oxide ions. Based on this assumption, the eq (5.5) can be simplified into eq
(5.6).73

4N5"2
AE

 

X(TIP) = (5.6)

The X(T1p) values obtained from the eq (5.2) are in emu per AxV205-nH20
which includes both V5+ and V4+ atoms. Of course, the V5+ atoms make
no contribution to the X0113). In order to calculate the AE of the V4+ ions,
the X(T1p) was normalized for the concentration of V4”/V5+ in the V205
framework. The latter is known from the alkali ion loading. Using the
corrected me) values into the eq (5.6), the AE energies were calculated
and are shown in Table 5.6. The values fall in the IR range and,
remarkably, electronic absorptions in the same range are observed

experimentally in the diffuse reflectance IR spectra of the compounds, see

176

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177

Table 5.6. Temperature-Independent Paramagnetism and Calculated and
Observed A5 for MxVZOS-rflO

 

Xq‘uu‘ AEroalcd) AE<obs<02

M x (emu/mole) (.cm‘l) (cm"1)

K 0.08 1.4.:1.0e-3 2500420 1900

K 0.26 8.5:3.8e-4 2130-813 2800(w), 1500(s)
K 0.33 1.2:0.3e-3 1100-660 1650

K 0.39 7.212024 19201090 1500

Cs 0.18 7.814.4e-4 2940-320 2450

Cs 0.28 1.0414120 830-520 1650

Cs (I 0.35 1.0:o.3e-3 1250-720 3000(w), 1590(5)
Cs 0.38 1.110.36-3 1270-760 V 1500

 

w : weak; 3: strong. lNormalized by the concentration of V4+N5+.

2Observed spectroscopically.

178

Figure 5.10. The AXV205-nH20 materials show a strong broad band in the
region of 1500-2500 cm-1 (Table 5.6). Some compounds even have an
additional band at ~3000 cm‘l, but it is considerably weaker. The bands
are absent in the spectra of V205 xerogel. This strongly supports that the
observed absorption bands are electronic d-dtransitions associated with the
V4+ centers. However, two closely spaced transitions are observed in
several phases suggesting that the real electronic structure is much more
complicated and the presence of possibly two kinds of V4+ ions originating
from different oxygen environments.

In AszOs-nHZO, the Curie constant, C, is expected to increase
linearly with the v4+ concentration. A linear relationship is indeed
observed in the range 0< x < 0.3 but beyond x ~0.3 the Curie constant
levels off and then declines somewhat at x ~0.55, see Figure 5.11. It is
interesting to speculate on the decline of the magnetic susceptibility beyond
x ~ 0.3. In Oka's model, the closest V—V distance is 3.0 A, involving,
dimers of vanadyl ions. As the number of spins introduced into the
vanadium oxide framework is increased, the V=O/V=O dimers are
populated by electrons. The loss of susceptibility may be due to spin
localization in these dimeric units followed by strong antiferromganetic
coupling which would lead to a diamagnetic or weakly paramagnetic
species. Such V=ON=O dimers with W“ centers are known in molecular
complexes and are all antiferromagnetically coupled. Examples include
[(VO(DANA)]29 [DANA = 1,5-bis(p-methoxyphenyl)-1,3,5-pentanetrione]
and [V2028e2(Sez)2].10 In fact, these antiferromagnetic dl-d1 interactions
seem to drive the formation of compounds. At low x values, the d1 centers
are relatively isolated and give rise to Curie paramagnetism. As the

number of these centers in the framework increases it is reasonable to

179

 

 

Reflectance

(b)

 

I I

1 T I r 1 I I
40003650330025026002250190015501200850

Wavenumber

 

Figure 5.10. Diffuse reflectance IR spectra of (a) KxV205-nIrI20 and (b)
KxV205-nH20. The broad peaks are assigned to electronic

transitions associated with V“ centers.

180

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0.00 ...,.r . r ”we“

 

 

. . ,fi . . , . . . 1 . .
O 0.1 0.2 0.3 0.4 0.5 0.6
x (Cs content)

Figure 5.11. Plot of Curie constant, C, vs x (alkali content)
for (a) KXVZOS-nIIZO and (b) CsxV205-nH20.

l8l

expect that beyond some value x, formation of dl—dl dimers will become
probable. Being antiferromagnetically coupled, the dimers will not
contribute significantly to the susceptibility. This will lead to a leveling off

or even a decrease of susceptibility at higher x values.

5.3.5. Electron Paramagnetic Resonance (EPR)

Spectroscopy

The increased number of V4+ centers in the V205 framework of
AXV205-nH20 is also reflected in the EPR spectra of these materials. The
pristine V205 xerogel shows a hyperfine structure due to a small amount
of V4+ (1: 7/2) impurities in an axially distorted crystal field.11 In
AszOs-nHzO, the increased V4+ centers enhance the spin—spin exchange
reaction which converts the original hyperfine structure into a symmetric
broad band with a g value centered at ca. 1.96. A typical EPR spectrum of
K0.33V205-nH20 is shown in Figure 5.12. The peak-width for all
AszOs-nHzO materials varies as a function of x as illustrated in Figure
5.13. Interestingly, a maximum peak width is also observed at x ~ 0.3,
consistent with the magnetic susceptibility data. This indicates that the spin
density in the reduced framework is decreasing after x > 0.3 due to
antiferromagnetic coupling and it is consistent with the magnetic data

discussed above.

5.3.6. Charge Transport Measurements

Samples of AxV205-nH20 were studied in a pressed pellet form by
dc electrical conductivity and thermopower measurements using the four-
probe geometry. Compared with V205 xerogel, the AxV205-nH20

materials show at least a one order magnitude increase in electrical

182

 

Intensity

 

 

 

I 1 1 I I I I I I W—r I I I I I I I

2800 3000 3200 3400 3600 3800
Gauss

Figure 5.12. Room temperature EPR spectrum of K033V205-nH20.

183

A
93
V

 

160,

150-3

1403 i

l
1
1301 }

Peak Width (G)

120—:

110%
3
100 r . . e, ..
0 0.1

 

 

' ' T I v I r I I T

, . . . . , .
0.2 0.3 0.4 0.5
x (K content)

 

(b)

 

160

d
.1

150-3 {

 

 

 

@140-j i f i}
1:. : 1
.6 u
«130—
3 g i
.25 .
°‘ ;
11oJ
1
100‘....,....,...-Tj...,....
0 0.1 0.2 0.3 0.4 0.5

x (Cs content)

Figure 5.13. Changes of EPR peak width as a function of
alkali ion loading for (a) Kszos-nHZO and (b)
CSXV205°HH20.

184

conductivity, to 10'3 - 10"2 S/cm at room temperature. Generally, the
conductivity slightly increases with the x as shown in Figure 5.14,
consistent with a small polaron semiconductor12 where charge transport is
due to electron hopping. Thus, conductivity increases with the number of
charge carriers (V4+) in the framework but levels off at x ~ 0.35. The
conductivity measurements on granular samples alone do not unequivocally
characterize their electrical behavior. A complementary probe to address
this issue is thermoelectric power (TP) measurements as a function of
temperature. TP measurements are typically far less susceptible to artifacts
arising from the resistive domain boundaries in the material because they
are essentially zero-current measurements. This is because temperature
drops across such boundaries are much less significant than voltage drops.
Figure 5.15 shows typical TP data for AszOs-nHzO as a function of
temperature. Accurate measurements at low temperature were hindered by
the very large sample resistances that developed. The Seebeck coefficients
for these materials are negative with big absolute values confirming a n-
type semiconductor. The Seebeck coefficients become less negative as the
x increases, also confirming the increased number of charge carriers with

V4+ concentration.

5.4. Conclusion

The use of bronze-like AxV205-nH20 phases has allowed the studies
of the reduced V205 xerogel framework without interference from the
intercalants. The optical and magnetic properties of these phases are
intriguing and associated with the environments and interactions of V4+
atoms in the V205 framework. These phases show relatively low d-d

electronic transitions occurring in the infrared range, which leads to small

Log 5 (S/cm)

185

 

-3
-4

-5

-8

 

IIII'IIIIIIIIIIIIIIIIIIIIIIIIIIIII

 

 

911111L11l111111111 1111L1L1

- 1 l
50 100 150 200 250 300 350
Temperature (K)

 

Figure 5.14. Four-probe pressed-pellet variable temperature electrical
conductivity data of (a) Ko,39V2Os-nH20 and (b) Ko.osV205-nH20.

lb
or

Thermopower (uV/K)
c'n
O

{I
01

186

 

 

 

 

: (a) 0086’ owydié’fg o
E (b) on a mom fig 0
: x “xxx
._ X :g’wx x
: x x x)“ {x xx ff“): )1 l
_ (C) xx )6" x x x x
100 h 1 1 1 l 1 1 X1 1 1 1 x g l 1 1 1 l 1 1 1
1 50 1 90 230 270 31 0 350

Temperature (K)

Figure 5.15. Variable temperature thermoelectric power data of
KxV205-nH20 : x = 0.39 (a), 0.33 (b) and 0.26 (c).

187

but significant temperature-independent paramagnetism. Similar
phenomena were also observed on all polymer/V205 intercalation
compounds”. These studies clarify that these phenomena originate from
the reduced V205 framework, not from the interactions between the
polymers and the framework. Interestingly, these AxV205-nH20 phases
show a maximal spin density at x ~ 0.3 suggesting the antiferromagnetic
coupling between spins when x > 0.3. The antiferromagnetic coupling is
common in vanadium compoundsz,9,10. The complicated magnetic
behavior of AxV205-nH20 suggests that it would be very difficult at this
time to obtain clear understanding of the spin interactions between

conducting polymers and V205 framework.

LIST OF REFERENCES

(l)

(2)

(3)

(4)

(5)

188

LIST OF REFERENCES

(a) Kanatzidis, M.G.; Wu, C.-G.; Marcy, H.O.; Kannewurf, C.R. J.
Am. Chem. Soc. 1989, 111, 4139—4141. (b) Wu, C.-G.; Kanatzidis,
M.G.; Marcy, H.O.; DeGroot, D.C.; Kannewurf, C.R. Polym. Mat.
Sci. Eng. 1989, 61, 969-973. (c) Kanatzidis, M.G.; Wu, C.-G.;
Marcy, H.O.; DeGroot, D.C.; Kannewurf, C.R. Chem. Mater. 1990,
2(3), 222-224.

(3) Murphy, D.W.; Christian, F.A.; Disalvo, F.J.; Waszczak, J.V.
Inorg, Chem. 1979, 1_8119), 2800-2803. (b) Chakraverty, B.K.;
Sienko, M.J. Phys. Rev. B 1978, l_7_(l_0), 3781-3789. (c) Gendell, J.;
Cotts, R.M.; Sienko, M.J. J. chem. phys. 1962, 31(2), 220-225.

(a) Babonneau, F.; Barboux, P.; Josien, F.A.; Livage, J. J. Chim.
Phys. 1985, _8_2, 761—766. (b) Bullot, J.; Cordier, P.; Gallais, O.;
Gauthier, M.; Babonneau, F. J. Non-Cryst. Solids 1984, 68, 135-
146.

(a) Legendre, J.—J.; Aldebert, P.; Baffier, N.; Livage, J. J. Colloid
Interface Sci. 1983, 94(1), 84—89. (b) Livage, J. Chem. Mater. 1991,
3, 573-593.

(a) Yao T.; Oka,Y.; Yamamoto, N. Mat. Res. Bull. 1992, 21, 669-
675. (b) Yao T.; Oka,Y.; Yamamoto, N. J. Mater. Chem. 1992,

(6)

(7)

(8)

(9)

(10)

(ll)

(12)

189

2(3), 331-336. (c) Yao T.; Oka,Y.; Yamamoto, N. J. Mater. Chem.
1992, 2(3), 337-340.

Abello, L.; Husson, E.; Repelin, Y.; Lucazeau, G. J. Solid State
Chem. 1985, :0, 379-389. ‘

(a) Drago, R.S. "Physical Methods in Chemistry" W.B. Sanders Co.:
Philadelphia, 1977. (b) Boudreaux, X.A.; Mulay, L.N. "Theory and
Applications of Molecular Paramagnetism", John Wiley and Sons:

New York 1976.

(a) Livage, J.; Gharbi, N.; Leroy, N.C.; Michaud, M. Mat. Res. Bull.
1978, _13, 1117—1124. (b) Stizza, S.; Davoli, I.; Benfatto, M J. Non-
cryst. Solids 1987, 95&96, 327-334.

Heeg, M.J.; Mack, J.L.; Glick, M.D.; Lintvedt, R.L. Inorg. Chem.
1981, 2_(), 833-839.

Liao, J .-H.; Hill, L.; Kanatzidis, M.G. Inorg. Chem. 1993, 32, 4650-
4652.

Sanchez, C.; Babonneau, F.; Morineau, R.; Livage, J.; Ballot, J.
Philos. Mag. B, 1983, 3, 279-290.

(a) Bullot, J.; Cordier, P.; Gallais, O.; Gauthier, M. J. Non—Cryst.
Solids 1984, 68, 123-134. (b) Livage, J.; Jolivet, J.P.; Tronc, E. J.
Non-Cryst. Solids 1990, 1_2_l_, 35-39.

190

(13) (3) Wu, C.—G. " Ph D. Dissertation" 1992, Michigan State
University. (b) Liu, Y.-J.; DeGroot, D.C.; Schindler, J.L.;
Kannewurf, C.R.; Kanatzidis, M.G. Adv. Mater. 1993, 3(3), 369—
372.

CHAPTER VI
POLYMERIZATION OF ANILINE AND N-PHENYL-IA-

PHENYLENEDIAMINE IN LAYERED METAL
PHOSPHATES BY AMBIENT OXYGEN

191

192

ABSTRACT

The formation of polyaniline in the layered metal phosphates,
HUOgPO4-4H20, a-Ti(HOPO3)2'HzO and a-Zr(HOP03)2-H20, is reported.
Aniline and N—phenyl—l,4—phenylenediamine (PPDA) are intercalated in the
layered phosphates to form the precursors for polymerization. X-ray
diffraction patterns show large interlayer expansions with titanium
phosphate and zirconium phosphate, indicating that a bilayer of amine
molecules are accommodated in the gallery. In contrast, only a monolayer
of amine molecules is intercalated in uranyl phosphate. After thermal
treatment at 130°C in air, the intercalated aniline and PPDA are slowly
polymerized by ambient oxygen. The formation of polyaniline was
confirmed by FT-IR, UV/V IS, EPR and magnetic susceptibility. Powder
X-ray diffraction shows that, after polymerization, the interlayer spacing
slightly increases from 10.46 to 11.8 A for anilinium/uranyl phosphate, but
dramatically decreases from 28.3 to 20.5 A for PPDA/zirconium phosphate
and from 18.87 to 13.25 A for anilinium/titanium phosphate. The
interlayer expansion is consistent with a monolayer of polyaniline present
in uranyl phosphate and titanium phosphate, and a bilayer of polyaniline in
zirconium phosphate. Gel permeation chromatography shows that the MW
of the intercalated polyaniline is much lower than that of bulk polyaniline.
Prolonged heating in air results in cross-linked polymer in the galleries.

All compounds are insulators.

193

6.1. Introduction

In recent years, inclusion of conjugated polymers into inorganic host
lattices has been the subject of considerable investigation},2 The lattices
provide confined spaces which can force the formed polymers into a
certain regularity, potentially enhancing charge transport. In such systems
the polymer chains are reasonably isolated from one another by the
inorganic material and may provide an opportunity to study
spectroscopically the properties of single chains.3

Polyaniline (PANI), a well-known conducting polymer4, has been
inserted into several inorganic hosts by different methods. One approach
uses hosts with sufficient oxidative power to intercalate and polymerize
aniline in situ. FeOCl5 and V205 xerogel6 are examples of such hosts.
However, this type of compounds are comparatively few, while most host
materials are non- or weakly oxidizing. Therefore, in order to polymerize
monomers inside host materials with insufficient oxidative power, external
oxidants must be used. Inoue and coworkers reported an electrochemical
polymerization of intercalated aniline in montmorillonite.7 Bein et al. used
(NH4)28203 to successfully polymerize the intercalated aniline in zeolites.8
The same method was also applied to M003.9 Another method to insert
conjugated polymers in host materials is to directly modify the oxidative
power of the host by incorporation of oxidants. By pre-intercalating Cu2+
in a host, an in-situ polymerization of aniline can be accomplished, as in the
case of silicates10 and in zirconium phosphate“. Recently, we reported
direct inclusion of polyaniline into M0S2 by taking advantage of the

exfoliation property of this dichalcogenide.12

194

Layered metal phosphates are known to possess rich intercalation
chemistry.13 The protons in the layers can be exchanged with cations or
neutralized with bases. The resulting intercalation compounds, depending
on the guest molecules, can have diverse properties.13,14 By first,
intercalating aniline and N-phenyl-l,4-phenylenediamine (PPDA)
molecules, we used oxygen to polymerize them topotactically to
polyaniline. In this method, the polymerization is carried out by simple
thermal treatment of the amine intercalated compounds in air. Traditional
oxidants such as (NH4)282Og, FeCl3, lead to ion-exchange reactions which
compete with the intralayer polymerization reaction and cause polyaniline
to form outside the hosts. With oxygen, the ion-exchange reaction is
totally avoided. We have already reported preliminary results from this
work in the case of uranyl phosphate.15 Here, we report the details of this
reaction and its application to or-titanium phosphate and or-zirconium

phosphate.

6.2. Experimental

6.2.1. Materials

Zirconyl chloride octahydrate (ZrOClz-SHzO), titanium
tetrachloride (T iCl4), aniline, and N-phenyl-l,4-phenylenediamine (PPDA)
were used as received from Aldrich Chemical Co., Milwaukee, WI.
Uranyl nitrate hexahydrate (UOz(NO3)2-6HzO) was obtained from J.T.
Baker Chemical Co., Phillipsburg, NJ. Phosphoric acid (85%) and
hydrofluoric acid (50%) were purchased from Fisher Scientific Co.,

Fairlawn, NJ. Catechol was received from Mallinckrodt Inc., Paris, KY.

195

Elemental analyses were done by Galbraith Laboratories, Knoxville, TN

and Oneida Research Services, Inc., Whitesboro, NY.

6.2.2. Measurements

Electronic absorption spectra were measured on a Hitachi U-2000
spectrophotometer from 1100 to 200 nm by spreading a Nujol mull of the
samples between two quartz slides.

Thermogravimetric analysis (TGA) was performed on Shimadzu
TGA-50. Typically 5-10 mg of samples were heated in a quartz crucible
from room temperature to 1000°C with 5°C/min in air or nitrogen.

Differential Scanning Calorimetry (DSC) used Shimadzu DSC-50
thermal analyzer. Samples (3-5 mg) were put in a aluminum pan and
heated to 200°C with 5°C/min. An empty aluminum pan was taken as the
reference.

Variable temperature magnetic susceptibility data were collected
from 5K to 300K on a S.H.E. corporation SQUID system at a magnetic
field of 400 gauss. The data were collected by diamagnetic components
obtained from the literature16 or the diamagnetic precursors.

Scanning Electron Microscopy (SEM) was done on JEOL-ISM 35
CF with an accelerating voltage of 15 KV. Samples were glued to the
microscope sample holder with conducting graphite paint.

Molecular weights were determined with a Shimadzu LC-10A HPLC
system with a PLgel 511 mix column. The measurements were done at 75°C
with NMP (containing 0.5 wt% LiCl) as the eluent. The elution rate was
0.2 ml/min. Polystyrene of known molecular weights was used as
standard. The detector was a UV/V is lamp which was set at 270 nm for

polystyrene and 315 nm for polyaniline. Roughly, an amount of 0.1 mg of

196

polyaniline was dissolved in 5 ml of NMP. The resulting purplish blue
solution was pre—filtered with a 4.5 1.1m of frit and then injected into the
column with a volume of 10 111.

The X-ray coherence length of the crystallites was calculated
according to the Scherrer's formula”: Lhkl = Kit/Boost). L is the
coherence length along directions perpendicular to the Miller index planes
(hkl), )1 is the wavelength of the X-rays used, K is Scherrer's constant and
has a value of 0.9, 0 is the Bragg angle, and B is the peak width at half-
height in radians.

The instruments and experimental setups for X-ray diffraction,
infrared spectroscopy and electron paramagnetic resonance (EPR) are the

same as those in chapter 2.

6.2.3. Preparation of Layered Metal Phosphates

HUOzPO4-4H20 (HUP), or-Zr(HOPO3)2-H20 (or-ZrP), and 01-
Ti(HOPO3)2~HzO (a-TiP) were prepared according to reported
methods.18,19,20 HUP is a luminous yellow solid which precipitates from
H3PO4 and UOz(NO3)2 in aqueous solution.18 or-ZrP is a white crystalline
powder prepared by adding concentrated H3PO4 to ZrOClz solution in
presence of HF.19 Crystalline or-TiP was synthesized by refluxing its gel in
concentrated H3PO4.20 The gel was prepared by slowly adding TiCl4 into
H3PO4 solution.

6.2.4. Preparation of (C6H5NH3)1,0UOzPO4-0.4H20
(AUP) and H0.12(C6HsNHC6H4NH3)0.ssU02PO4 (AzUP)

Excess aniline or PPDA was added into a flask containing 1.0 g of
HUOzPO4-4HzO and 80 ml of distilled water. The mixture was stirred for

197

one day at room temperature. The product was filtered and then washed
with acetone. After drying overnight under N2, AUP is pale yellow and
AzUP is pale gray. Anal. Calcd for (C6H5NH3)1,0UOzPO4-0.4H20: C,
15.40%; H, 1.89%; N, 3.0%. Found: C, 15.48%; H, 1.78%; N, 2.95%.
The composition of A2UP, calculated from thermogravimetric analysis

(TGA), is H0.12(C6H5NHC6H4NH3)0.88U02PO4.

6.2.5. Preparation of H0,6(C6H5NH3)1,4T1(PO4)2 (ATiP)

An amount of 1.0 g (3.88 mmol) of Ti(HOPO3)-HzO and 1.44 g
(15.48 mmol) of aniline were introduced into a 23 ml autoclave. The
autoclave was put into a furnace with a constant temperature of 130°C for
3 days. After cooled to room temperature, the white product was filtered

and washed with acetone. The composition of ATiP, calculated from TGA,
is H0.6(C6H5NH3) 1.4Ti(PO4)2.

6.2.6. Preparation of H0,7(C6H5NH3)1,3Zr(PO4)2 (AZrP)

and H0.6(C6H5NHC6H4NH3)1.4Zr(P04)2 (A2ZrP)

Excess PPDA or aniline was added to Zr(PO4)2-H20 (0.5 g) in 50
ml of distilled water, and the mixture was stirred for two days. The
reaction temperature was ~25°C for aniline and 80°C for PPDA. The

products were removed by filtration, washed with acetone, and then dried

under N2. AZrP is white and Azer is pale gray. Anal. Calcd. for
Ho,6(C6H5NHC6H4NH3)1,4Zr(PO4)2: C, 37.3%; H, 3.5%, N, 7.26%.

Found: C, 37.6%; N, 7.03%; H, 3.54%. The composition of AZrP,
calculated from TGA, is Ho,7(C6H5NH3)1,3Zr(PO4)2-0.1H20.

198

6.2.7. Preparation of (PANI)0,94UOzPO4-0.5H20 (PUP),

(PANI)0,3Ti(PO4)2 (PTiP) and (PANI)2,4Zr(PO4)2

(PZrP) from AUP, A2ZrP and ATiP

Quantities of AUP, Azer and ATiP were introduced into small
pyrex containers and the containers were put into a furnace with a constant
temperature of 130°C. After several weeks, black products were obtained.
Anal. Calcd. for (PANI)0,94UOzPO4-0.5HzO: C, 14.7%; H, 2.86%, N,
1.24%. Found: C, 14.1%; N, 1.27%; H, 2.83%. Anal. Calcd. for
(PANI)2.4Zr(PO4)2: C, 36.67%; H, 2.7%, N, 7.1%. Found: C, 38.78%;
N, 6.52%; H, 2.69%. The composition of PT iP, calculated from TGA, is
(PANI)0.gTi(PO4)2.

6.2.8. Extraction of Polyaniline from PUP
PUP (0.1 g) was added to excess 20% HCl solution. After one day
of stirring at room temperature, the black precipitate was collected by

filtration, washed with water then with acetone, and dried in air.

6.2.9. Extraction of Polyaniline from PTiP

PT iP (0.1 g) was added to 50 ml of 20 % HCl solution containing 1.5
g of catechol. The mixture was refluxed for 2 days and then cooled to
room temperature. After filtration, the black residue was washed with

water and acetone, and dried in air.

6.2.10. Extraction of Polyaniline from PZrP
An amount of 0.2 g PZrP was added to excess 10% HF solution.
After ~12 hours of stirring, the black precipitate was filtered, washed with

water then with acetone, and dried in air.

199

6.2.1]. Preparation of Base Form of PANI
Extracted PANI was treated with excess 0.1 M NH40H for ~12
hours. The product was filtered, washed copiously with distilled water and

acetone, and dried in air.

6.3. Results and Discussion

6.3.1. Characterization and Polymerization of Aniline-

and PPDA-lntercalated Compounds

The reaction of layered metal phosphates with aniline or derivatives
results in intercalation compounds with well defined X-ray powder
diffraction patterns. For example, the X-ray diffraction patterns of
H0.7(C6H5NH3)1.3Zr(PO4)2 (AZrP) and
H0_6(C6H5NHC6H4NH3)1.4Zr(PO4)2 (A2ZrP) are given in Figure 6.1.
Several strong (001) peaks, associated with the stacking axis perpendicular
to the layers, are observed indicating that the intercalants are highly
ordered. The first diffraction peak (001), corresponds to an interlayer
distance, of 19A for AZrP and 28.3A for A2ZrP. Subtracting the layer
thickness of ~6.6A, AZrP and AZZrP show net expansions of 12.4A and
21.7A, respectively, which are consistent with the expected expansion from
a bilayer of aniline and PPDA molecules in the interlayer regions. It is
likely that the molecules are slightly tilted or interdigitated. The interlayer
distances and compositions of all compounds are summarized in Table 6.1.

Ho,6(C6H5NH3)1,4Ti(PO4)2 (ATiP) also has bilayered anilinium molecules

in the interlayer space. However, no intercalation was observed between

200

 

 

 

Intensity
3'3

 

 

M A AAA AA A..— ._ _g
—-‘ ‘—

IIIIIIIIIIITIIIIIIIIIIIIrIIII

0 10 20 30 40 50 60
2 Theta

 

 

 

 

Figure 6.1. Powder X-ray diffraction patterns of (a) or-Zr(IIOPO3)2-HZO,
(b) H0.7(CsHsNHs)1.3Z1‘0’04h and (C) 110.6(C6HSNHC6H4NH3MAZI'1PO412-

201

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202

PPDA and TiP. In contrast to the group Vl phosphates above,
(C6H5NH3)1.0U02PO4-0.4H20 (AUP) and
Ho,12(C6H5NHC6H4NH3)0_88U02PO4 (A2UP), show much smaller net
expansions suggesting the presence of a monolayer of organic guests.

When these materials were heated at 0 130°C in air, their color
gradually changed from yellow or pale gray to dark green and finally to
black. The procedure took 4 days for AUP, 8 days for ATiP, and only one
day for A2ZrP and AZUP. The color change is, indeed, associated with the
polymerization of aniline and PPDA. This is confirmed by FT-IR
spectroscopy which shows that the vibration bands of the monomers and
dimers gradually decrease in intensity while the vibration bands of PANI
quickly dominate the spectra. The changes in the FT-IR spectra of AUP
during polymerization are shown in Figure 6.2. Before thermal treatment,
AUP shows the characteristic vibrations of anilinium at ~3000, 2600, and
1500 cm-1, consistent with an acid-base intercalation reaction, where the
protons transfer from the layers to aniline. However, the appearance in the
spectrum of broad vibration bands at 3490 and 3380 cm-1, and a doublet at
~750 and ~690 cm‘l also implies the presence of neutral aniline in the
layers. After one week, the absorption bands at ~3400-~2800 cm-l
(originating from the OH, NH3+, and NH2 groups) weaken and then are
completely masked by a strong electronic transition from PANI, which
starts from ~1800 cm”1 and extends to the visible region. At the same time,
the IR spectrum of PANI is clearly observed. In three weeks, the vibration
bands of anilinium disappear. Under the same conditions, the complete
polymerization process took ~4 weeks for ATiP, but never went to
completion for Azer and AzUP. The FT-IR spectra of the last two

compounds still show significant amounts of the intercalated dimers. The

203

 

 

(b)

Intensity

(C)

 

 

 

' r ' l ' ' ' l ' ' ' l ' ' '
4000 3100 2200 1300 400
Wavenumber

Figure 6.2. FT-IR spectra of (C6H5NH3)L0U02PO4.0.4H20 (AUP) under
thermal treatment for (a) 0 week, (b) one week, and (c) three weeks.

204

FT -IR spectra of the polymers extracted from the framework are shown in
Figure 6.3, where the characteristic vibrations of bulk PANI (emerldine
form) are clearly observed in all cases, confirming that they are PANI.
Their frequencies and corresponding vibration modes are listed in Table
6.2. Compared with bulk PANI, the frequency and shape of the extracted
PANI are respectively slightly higher and sharper. This is either due to the
shorter polymer chain length (see below) or to the formation of cross-
linked PANI, which has been reported to form when PANI is heated.20
Although color changes were also observed for AZrP, the FT -lR spectrum
of the extracted species, surprisingly, is not PANI. The band at ~1300 cm-1
is weak and the bands at ~1100 and ~800cm-1 are nearly absent, indicating
that the C-H vibration is inhibited. One possibility is that the polymer
chains are heavily cross-linked.

Under the same polymerization conditions, these precursors sealed in
evacuated tubes show no color changes which indicate no polymerization
occurred, confirmed by FT-IR. This can be seen by TGA and DSC
experiments under oxygen and nitrogen atmosphere, as shown in Figure
6.4 and Figure 6.5, respectively. The precursors have better thermal
stability under oxygen than under nitrogen because of the PANI formation
during the experiment. For A2ZrP, the weight loss begins at 250°C under
nitrogen, but mainly at 400°C under oxygen. For ATiP, the weight-loss
begins at ~200°C under nitrogen flow. However, under oxygen flow, two
decomposition steps were observed at ~200°C and ~400°C. The weight loss
starting at 200°C is attributed to aniline and was confirmed by mass
spectrometry. The loss of aniline would slow down the intralamellar
polymerization and result in incomplete polymerization. In addition, DSC

of A2ZrP shows a slight endotherm to 200°C under N2 atmosphere

205

 

(b)

Intensity

 

 

 

T I F j l I I

I . .
2200 1300 400
Wavenumber

, .
4000 3100

Figure 6.3. FT-IR of extracted PANI from (a) PUP, (b) PZrP and (c) PTiP,
and (d) bulk PANI.

206

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Weight %
8

 

 

 

 

 

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60%
l

50 "'F"'I"*IT"I"'
0 200 400 600 8001000

Temnemture (0C)

Figure 6.4. Thermogravimetric analysis diagrams of (a) PZrP and (b) PTiP
under air (—) and nitrogen flow ( ----- ).

mW

208

 

 

 

 

-1.0fi"'lT"‘l""l"
0 50 100 150 200 250

Temperature (C)

 

Figure 6.5. Differential scanning calorimetry of A2ZrP under 02 (----)
and N2 (_).

209

consistent with the loss of PPDA. However, an exotherm was observed at
~ 180°C under oxygen, consistent with polymerization of PANI.

The significant finding was that oxygen is the key for the
intralamellar polymerization. Furthermore, attempts to polymerize the
intercalated monomers with other oxidants such as (NH4)28203 and FeCl3
did not yield intercalated PANI, instead ion-exchange was observed

followed by polymerization on the particle surface.

6.3.2. UVIVis Spectroscopy

The UV/V is spectrum of (PANI)0,94U02PO4-0.5H20 (PUP) shows a
very broad band at ~ 750 nm as shown in Figure 6.6. The band is the
characteristic polaron absorption of protonated PANI.22 The same band
was also observed at ~ 800 nm for (PANI)2,4Zr(PO4)2 (PZrP) and
(PANI)0.3Ti(PO4)2 (PTiP). This is consistent with infrared spectroscopic
data confirming the formation of protonated PANI inside the galleries of

layered metal phosphates.

6.3.3. X-ray Diffraction

The intralamellar polymerization changes the orientation of the
intercalated molecules and hence leads to a change of the interlayer distance
of the host. Therefore, the polymerization can be monitored by X-ray
diffraction measurements. The X-ray diffraction patterns of AUP as a
function of time are shown in Figure 6.7 where, as the reaction proceeds,
the peaks due to AUP gradually disappear and the peaks due to PUP
become evident. The peaks due to AUP disappear completely in three
weeks, consistent with the infrared spectroscopic data (described above).

After polymerization, the interlayer spacing slightly increased to 11.8 A

210

 

(a)

 

 

(b)

 

Absorbance

 

(e)

 

 

 

l l 1 l l
200 400 600 800 1000
nm

Figure 6.6. Electronic absorption spectra of (a) PUP, (b) PZrP, and (c)
bulk PANI.

Intensity

211

 

 

__L_J.

3147”:

 

 

41‘ K (C)

 

 

 

 

 

2 Theta4

Figure 6.7. Evolution of powder X-ray diffraction patterns of

(C6H5NH3)L0U02PO4.0.4H20 (AUP) under thermal treatment for (a) 0 week,

(b) one week, (c) two weeks, and ((1) three weeks.

 

212

for PUP. However, it dramatically decreased to 20.5 A for PZrP and
13.25 A for PTiP. The net expansion of PZrP is ~13.9 A, comparable
with a bilayer of PANI molecules in the interlayer regions as illustrated in
Scheme 1. On the other hand, PTiP has a net expansion of only ~6 A
which suggests a monolayer of PANI molecules as illustrated in Scheme 2.
In all cases the X-ray diffraction peaks become broader after
polymerization due to a decrease in crystallinity. As estimated from the
Scherrer formula, the coherence length along the layers stacking axis
decreases from ~600 A in AUP to ~180 A in PUP, from ~400 A in ATiP
to 180 A in mp and from 260 A in A22rP to 200 A in PZrP. This is
attributed to the increased stacking disorder during polymerization which
involves significant movement of monomers and diffusion of oxygen and

water in and out of the materials.

6.3.4. Magnetic Properties

The diamagnetic hosts allow the observation of the evolution of the
EPR spectroscopic polaron signal of PANI during the polymerization. All
precursor compounds are EPR silent. As the reaction proceeds, the
compounds start to show symmetric EPR signals which gradually increase
in intensity as shown in Figure 6.8. The peak widths of these signals
decrease with reaction time, indicative of extensive electron delocalization
and consistent with polaron formation in PANI. Thus, peak width (Apr)
decreases from 12 to 8 G in PUP, from 7 to 2 G in TiP, and from 15 to 12
G in ZrP. The g values are close to the free electron value of 2.0023.
These observations are consistent with the gradual growth of PANI. Bulk

PANI in a protonated form was reported with a peak width about < 3 G,23

213

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Intensity

 

 

 

 

 

I I I I l I I I I I I I I I l I I I I I I I I I

3200 3210 3220 3230 3240 3250
Gauss

Figure 6.8. Electron paramagnetic resonance spectrum of ATiP after one
week (----) and three weeks (—-) of thermal treatment.

216

however, the value can be > 10 G with other dopants24 and also depends on
the relative ambient moisture.

The polymerization process was also monitored with magnetic
susceptibility measurements. The evolution of magnetic susceptibility of
AUP as a function of reaction time and temperature are shown in Figure
6.9. Before thermal treatment, AUP is diamagnetic. When heated, its
magnetic susceptibility begins to increase and shows a temperature-
dependent behavior. However, the relationship between magnetic
susceptibility (Xm) and temperature does not follow the Curie-Weiss law.
This is probably due to the presence of the Pauli susceptibility which is
observed in bulk PANI.25 Similar data were also obtained for PTiP and
PZrP. The Pauli susceptibility and Curie spin density data (calculated from
the susceptibility) are summarized in Table 6.3. Except for PUP, the Pauli
susceptibility data of PT iP and PZrP are consistent with reported values
which increase with protonation and show a range from 0 to 6.0xe'5
emu/mole. The Curie spin density at PUP and PT iP is approximately one
spin per 60 rings and only one spin per 135 rings at PZrP. This is
probably because of incomplete polymerization in PZrP where the spin

density is diluted by the diamagnetic dimers.

6.3.5. Thermogravimetric Analysis Studies

TGA diagrams of PUP, PTiP and PZrP under 02 are given in
Figure 6.10. PZrP and PT iP show a single-step weight-loss beginning at
400°C. PUP shows a small weight loss below 100°C, attributed to water,
and two major weight-loss steps at 400°C and 600°C. The weight-loss step
starting at 400°C is attributed to the loss of the intercalated PANI as it
thermally breaks up. Compared to bulk PANI in its doped form26 (<

217

 

 
  

 

 

 

 

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5, 4.0104
AUP/PUP
X20104 AUP ‘
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0 50 100 150 200 25'0 300
Temperature (K)

Figure 6.9. Variable temperature magnetic susceptibility data of (a) AUP,
(b) AUPIPUP, and (c) PUP.

218

Table 6.3. Pauli Susceptibility and
Curie Spin Density of PAN I/Metal

Phosphate Intercalates

 

Pauli susceptibility

Curie spin density

 

Compound (emu/mole) (ring per spin)
PUP 1.3e'4 55
PTiP 4.4e'5 66
PZrP 8.0e’5 135

 

219

 

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Temperature(°C)

A
O

V

c:

 

Weight %

 

 

 

70--.,...,...,...T..-
0 200 400 600 800
Temperature(°C)

Figure 6.10. Thermogravimetric analysis diagrams under oxygen for (a)
PTiP, (b) PZrP, and (c) PUP.

220

250°C), the intercalated PANI molecules show superior thermal stability,
which is due to the spatial confinement and separation of polymer chains by
the metal phosphate layers. X-ray diffraction confirms that the final
residues at 900°C are (U02)2(P207), ZrP207, and TiP207. Calculated
from the diagrams, the composition is (PA-Nl)2,4Zr(OPO3)2 for PZrP,
(PANl)o,3Ti(OPO3)2 for PTiP, and (PANI)0,94U02PO4-0.5H20 for PUP,
consistent with the elemental analyses. Significant amounts of intercalants
were lost during polymerization of ATiP and Azer, but almost none in
AUP. This is consistent with the dramatic decrease of the interlayer
spacing at PTiP and PZrP.

6.3.6. Scanning Electron Microscopy (SEM)

Figures 6.11 and 6.12 illustrate SEM micrographs of the layered
metal phosphates before and after intercalation. Clearly, all metal
phosphates show plate-like morphology, consistent with their layered
structure. The average particle size of uranyl phosphate is slightly larger
than those at zirconium phosphate and titanium phosphate. The particles of
the latter are in the sub-micrometer range regime. After intercalation, the
plate-like morphology and average particle size are maintained. After
oxidative polymerization, the shape and size of the particles, compared
with their precursors, were also unchanged, see Figure 6.13. These SEM
micrographs confirm the crystalline nature of the inclusion compounds and

are consistent with a topotactic polymerization inside the layers.

6.3.7. Gel Permeation Chromatography (GPC) Analysis
The extracted PANI from any of the inorganic hosts was partially

soluble in NMP. Therefore, the molecular weight of the soluble portions

221

Figure 6.11. SEM micrographs of layered metal phosphates
before and after intercalation : (a) HUP, (b) a-ZrP and (c) or-
TiP.

222

 

223

Figure 6.12. SEM micrographs of layered metal phosphates
before and after intercalation : (a) AUP, (b) A2ZrP and (c)

ATiP.

224

 

225

Figure 6.13. SEM micrographs of (a) PUP, and (b) PZrP and
(c) PTiP.

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227

was determined by GPC. The GPC chromatographs of the three extracted
PANI materials are shown in Figure 6.14 where one asymmetric elution
band is observed in all cases. The MW of the extracted PANI is
summarized in Table 6.4. All values are much lower than that of bulk
PANI prepared chemically or electrochemically which is in the range of
32,000.21b27 It is also clear that the MW of PANI from A2UP is higher
than that from AUP, however, the latter is more uniform. In order to
monitor the progress of the polymerization in the intralamellar space of the
U02PO4 we stopped the reaction at regular intervals, extracted the
polymer from the host and determined its MW by GPC. Surprisingly, we
found that the MW of the soluble fraction decreases with reaction time.
For example, PUP shows that the Mw is ~14,000 (Mn = ~4400) in the first
week and decreases to ~7400 (Mn = ~4,500) at the second week and only to
~4,500 in the end of the third week. We also observed that the NMP-
soluble fraction decreased with prolonged polymerization time. This result
suggests that , as the MW increases and a certain amount of cross-linking
occurs, the polymer becomes insoluble and that in each case above the
soluble fraction is what is left over. The reason the MW of the soluble
fraction is smaller in samples that have been heated for a longer time is
because it represents kinetically trapped oligomers or short polymer chains

in pockets of cross-linked high MW polymer.

6.3.8. Charge Transport Properties

Since the conjugated polymers are embedded in the insulating host
and cannot be accessed electrically, all PANI intercalated materials
described are insulators. This behavior is similar to that of the systems

which involve insulating materials as hosts.7,8

228

 

 

 

Intens1ty
A
C"
v

 

i
(c) A.

II—TITIII r3()rrlrrr

0 10 60
Reztention3 time (min)5

 

 

 

 

 

Figure 6.14. GPC chromatographs of extracted PANI from (a) PUP, (b)
PTiP and (c) PZrP.

229

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6.4. Conclusion

We have successfully synthesized polyaniline in layered metal
phosphates by thermal treatment in ambient oxygen. The spectroscopic and
magnetic data of the extracted PANI are comparable with those of bulk
PANI prepared chemically. However, there is evidence of cross-linked
between molecules in the intralamellar space. The use of PPDA as a
monomer for PANI did not yield shorter reaction times. The results
reported here indicate that oxygen may be a convenient and clean reagent
for topotactic oxidative polymerization of monomers occluded in inorganic

galleries.

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(2)

(3)

(4)

231

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