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This is to certify that the

thesis entitled

Feasibility Study on the Application of a

Film Based Thermal Sensor

presented by

John Gerald Betts

has been accepted towards fulfillment
of the requirements for

M.S. Chem. Eng.

degree in

 

 

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Major professor

Date j/f/73

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FEASIBILITY STUDY ON THE APPLICATION
OF A FILM-BASED THERMAL SENSOR

By

John Gerald Betts

A THESIS

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

MASTER OF SCIENCE

Department of Chemical Engineering

1993

ABSTRACT

FEASIBILITY STUDY ON THE APPLICATION
OF A FILM-BASED THERMAL SENSOR

By

John Gerald Betts

Many industries depend on products that require specific
temperature control and storage. With this dependence in view, an
alternative to electronic thermal monitoring has been proposed
utilizing a film-based chemical sensor. A titanium based film on a
glass substrate will react with a catechoI-Iike compound giving a
colorimetric measurement. This color change can be used
qualitatively and quantitatively to determine the time-temperature
history of products. Use of this sensor appears feasible in the
temperature range of 65 to 140°C for time-temperature monitoring;
however, use in the -20 to 30°C temperature range only appears
feasible for the determination of the maximum temperature
achieved. An indicator for temperatures between 30 and 65°C may
also be feasible, based on the performance of the high temperature
senson

This work is dedicated to my parents, my sister, and especially to
Julie without whose support this work would not have
been possible. -

iii

ACKNOWLEDGEMENTS

I would like to express my deep sense of gratitude to my
advisor, Professor Kris Berglund, for his encouragement and
guidance throughout the course of this work.

I would also like to thank Drs. Beatrice Torgerson and Joel
Dulebohn for their assistance and background work used for this

project.

iv

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

1. INTRODUCTION
1 .1 Scope
1 .2 Preview

2. LITERATURE SURVEY
2.1 Current sensors
2.2 Films
2.3 Indicator Chemicals
2.4 Solvents

3. MATERIALS
3.1 Films
3.2 Indicator Chemicals
3.2.1 Low Temperature
3.2.2 Elevated Temperature
3.3 Solvents

4. RESULTS

4.1 Low Temperature Sensor
4.1.1 Construction and Materials
4.1.2 Cleaning and Quenching
4.1.3 Results and Discussion

4.2 Elevated Temperature Sensor
4.2.1 Construction and Materials
4.2.2 Cleaning and Quenching
4.2.3 Results and Discussion

viii

income

10
14
14
19
19

21
21
23
25
28
28
34
35

5. CONCLUSION

6. RECOMMENDATIONS FOR FUTURE WORK

7. APPENDIX: RAW DATA

8. LIST OF REFERENCES

vi

54

56

57

63

Table
Table
Table
Table
Table

Table

Table

Table
Table

Table

Table

(II->03“)

A-2

A-3

LIST OF TABLES

Original film composition.
Current film composition.
Zirconium film composition.
Solvents and their melting points.

Qualitative determination of indicator
chemicals for the high temperature sensor.

Feasibility of indicator chemicals for high
temperature sensors.

Average relative absorbance of film product
data reacted in catechoI/wax solutions at
studied temperatures.

So and k' results of fit.

Raw data of the absorbance of titanium film
colored product reacted in catechoI/paraffin
wax solution.

Raw data of the absorbance of titanium film
colored product reacted in catechol/IRM #8618
wax solution.

Raw data of the absorbance of titanium film
colored product reacted in catechol/IRM Hewax
wax solution.

vii

11
12
12
20

30

33

43
49

57

59

62

Figure
Figure
Figure
Figure

Figure
Figure

Figure

Figure

Figure

Figure

Figure

Figure

b-CON

U!

10

11

12

LIST OF FIGURES

Sensor schematic.
Sol-gel products flowchart.
Titanium alkoxide/carboxylic acid reaction.

Hydrolysis and condensation reaction of
titanium alkoxide.

Chemical structure of indicators.

Absorbance as a function of time for pyrogallol
and catechol in diethyl fumerate reacted with
titanium film at 32°C.

Relative absorbance-time profile of
catechol/dimethyl succinate solution
reacted with the titanium film at 32°C.

Relative absorbance-time profile of
Catechol/dimethyl fumarate solution
reacted with the titanium film at 32°C.

Kinetic results of catechol/paraffin wax
solution reacted with titanium based film
at 65°C.

Absorbance versus wavelength for
catechol/IRM #8618 wax solution reacted
at 100°C for 10 minutes.

Average absorbance of the colored film
product of the catechol/IRM#8618 wax
solution reacted at 100°C.

Absorbance of film product vs. time for
three catechol/paraffin wax solution runs
at 65°C.

viii

15

22

26

27

32

38

39

41

Figure

Figure

Figure

Figure

Figure

Figure

13

14

15

16

17

18

Average relative absorbance and least
squares data fit of titanium film product
reacted in catechol/saturated paraffin wax
for all temperatures studied.

Average relative absorbance and least
squares data fit of titanium film product

reacted in catechol/unsaturated paraffin wax

for all temperatures studied.

Average relative absorbance and least
squares data fit of titanium film product
reacted in catechol/IRM #8618 wax

for all temperatures studied.

Average relative absorbance and least
squares data fit of titanium film product
reacted in catechol/IRM Hewax for all
temperatures studied.

In(k’) versus 1/T from titanium film reacted
with catechol/IRM #8618 wax solution.

In(k’) versus 1/T from titanium film reacted
with catechol/paraffin wax solution.

ix

45

46

47

48

51

52

1. INTRODUCTION

1.1 Scope

Many processes depend on raw materials that must be stored
at specific temperatures. Composite prepregs, frozen food storage,
and thermal food preparation are all examples of fields that rely on
keeping materials at specific temperatures. Quality control and
safety assurance of these products may be determined by the
thermal history profile. Several types of technologies exist for
measuring the time-temperature profile of substances. These
processes are expensive, complicated, or lack quantitative
information on the time-temperature history. The development of an
inexpensive, reliable, qualitative and quantitative time-temperature
sensor would allow more effective and controlled use of materials
that are stored or processed under strict thermal conditions.

1.2 Preview

The initial thrust of this project was the determination and
construction of a cold time-temperature sensor. We intended to
produce a film-based colorimetric indicator that could be used
qualitatively and quantitatively to determine the time-temperature
history of a storage or processing environment. Indicator chemicals
were to be dissolved in solvents that had melting points ranging
from -20°C to 19°C. These indicator solutions would then be frozen
to the film covered substrate. The completed unit of substrate,
film, and indicator solution would comprise a time-temperature
sensor specific for the melting point of that solvent. The use of
multiple sensors with solvents of different melting points was
desired to give a detailed time-temperature history profile. As the
individual solvents reach their melting point temperature, the
indicator chemical will begin reacting with the film causing the
film to turn color. A schematic of this sensor is shown in Figure 1
(on the following page). Absorbance studies of the color change
intensity and kinetic reaction data could be used to calculate the

IQ

rFrozen solvent with dissolved
indicator chemical

 

Film layer —>

 

Transparent substrate 3
Figure 1 Sensor schematic.

thermal history of the sensor. The requirements for this low-
temperature sensor would include: quantitative and qualitative color
change of the film and Quenched reaction below solvent melting
point.

Synthesis of the film, determination of a suitable indicator
chemical, and solvent studies were required and performed to
determine a suitable low-temperature sensor. Problems developed
with these cold temperature sensors, including poor quenching of the
color change reaction after returning to temperatures below the
solvents melting point. Therefore, subsequent studies were focused
on a high temperature sensor with the hope that these problems
could be minimized. High temperature sensors have also received
less attention than the cold temperature sensors as indicated by the
availability of commercial products(Taoukisl). The second
alternative use of this approach, an elevated temperature sensor, if
practical, would also greatly benefit many industries, especially the
food processing companies.

Currently, monitoring of sterilization is done manually by
quality control personnel, and very little information on the
temporal component is obtained. The advantage of the proposed high
temperature sensor would be to record and store the time-
temperature exposure profile of a process by means of a colored
chemical reaction. The optical reading from the sensor can then be

3
integrated and related to calibration curves to validate the process.
Additionally, since this proposed sensor would be used for on-line
validation of thermal processing, the color change reaction would
not have to be completely quenched. Quenching of the reaction would
not be important since measurements are made immediately
following processing. This contrasts with the cold-temperature
sensor since for storage processes at low temperatures the sensor
may not be measured until days after the storage temperature
exceeded the melting points of the solvents.

The high temperature sensor is identical in design to the cold
temperature sensor, with the exception of different solvents with
melting points ranging from approximately 65°C to 120°C. In this
work, determination of the appropriate indicator chemicals,
solvents, and films were accomplished for this temperature regime.
Kinetic studies over the temperature range of 65°C to 140°C were
performed. The resulting data was analyzed using a kinetic model
which is based on a first order rate law describing consumption of
the reactive sites in the film in an attempt to construct suitable
calibration curves. Results of the analysis indicate that the sensor
does appear to generally follow a first order type kinetic rate
expression. These results indicate that the high-temperature film-
based sensor may be a feasible method for determining the time-
temperature profile of materials. Ultimately, useful calibration
curves need to be established before the proposed device can be used
as a commercial sensor.

2. LITERATURE SURVEY

2.1 Current Sensors

The determination of the time-temperature history of
materials is an area that has used a variety of technologies in the
creation of sensors. Enzymatic, acid-base, diffusion, electronic, and
combinations of these types can all be used to determine the time-
temperature history of a substance. The sensors that have been
examined deal almost exclusively with low temperature (frozen food
storage) conditions. A good introductory reference about these low
temperature sensors is a paper by Taoukisl. Examination of the
sensors based on these different techniques will illustrate one or
more drawbacks in the determination of the time-temperature
profiles of the environment.

Enzymatic indicators have been patented by Blixt2 and
Agerhem3, among others. This type of sensor uses a color change
indicator based on the change in pH caused by a controlled enzymatic
reaction. The enzyme is physically separated from the substrate and
indicator by means of a breakable barrier. Once this barrier is
broken, the enzyme and substrate/indicator are allowed to mix, and
the reaction is started. The indicator's pH measurement can give the
time-temperature profile of the sensor if the enzyme activity is
included. As temperature increases, enzyme activity increases, and
the pH will change at an accelerated rate. Drawbacks of this sensor
technology include denaturing of the enzyme at extreme
temperatures and the requirement of physical destruction of the
separation barrier.

Shafer4 and Jalinski5 have both patented an acid-base thermal
exposure indicator used to determine the expiration of shelf-life of
materials. This device uses a chemical that reacts at a rate
depending on time, temperature, and pH to produce an amine. An
indicator chemical is also incorporated into the sensor which reacts

4

5
independently, depending on time, concentration, and pH. Once one of
these chemicals is consumed, an acid-base reaction occurs, and the
rapid change in pH causes a color change. This indicates the
completion of the two independent reactions. Variations of the
concentrations of these chemicals can be used to create a sensor for
materials with a specific shelf-life at a specified temperature. The
ambient temperature controls the reaction rate. The concentrations
of the reactants control the length of time until the end-point of the
reaction is reached. Since this indicator uses an end-point, no
information on the time-temperature history of the sample can be
obtained.

Several types of diffusion-based sensors have been studied and
patented. ManskeG, Patel7i3i9, Allmendinger“), and Arens“, among
others, have all patented a diffusion-based, time-temperature
device. Manske uses a fluid pad attached to a wick containing an
indicator to measure the progress of the fluid. Patel has indicators
that use both liquid and vapor diffusion through a medium to
measure time-temperature profiles. The reactant moves through a
porous medium reacting with an indicator, giving rise to a visible
moving boundary. Allmendinger has produced a device suitable for
six month storage times of frozen foods, using a diffusion based
system. Arens utilizes a rubbery polymer that diffuses and renders
transparent the diffusion barrier. These indicators all have one or
more of the following drawbacks; relatively complicated design,
endpoint indication or lack of time-temperature profiles, and
physical activation by removing a barrier required.

Electronic time-temperature indicators range from computer
monitoring using thermocouples, to Kang's12 process of
electrochromatic reactions. Computers can be interfaced to
thermocouples and used to monitor the time-temperature profile of
materials. Karr13 uses a small integrated circuit and galvanic
consumable electrode as a coulometric indicator. This charge
transfer is the electronic equivalent of change in reaction rate as a
function of temperature. Lastly, Kang12 uses an electrochromic

6
diffusion material that changes color as electrons diffuse from the
electron source to the electron sink. These methods are all
relatively complex, and assumed to be expensive to manufacture.

2.2 Films

The films required in this study must be optically clear,
resistant to solvents, reactive with the indicator, and able to give a
homogeneous coating on a substrate. Sol-gel chemistry is a field
that can produce materials in different forms: solutions, films, and
gels. Titanium is a metal that may form metal-ligand bonds with a
possible corresponding color change. Combining these two factors,
Anderson14 and Dunuwila15 discuss the formation of a membrane or
film coating made from inorganic titanium oligimers with attached
organics using controlled hydrolysis of titanium alkoxides in water
and acids. The generalized sol-gel process, as illustrated in Figure
2 (on the following page), is reproduced from Anderson”. The
abundance of possible routes in the sol-gel process indicates that
specific procedures must be followed to yield the product of choice.

Three types of reactions may occur in the preparation of sol-
gel inorganic films: acid reactions, hydrolysis, and condensation
(Kirk-Othmer15). The ratios of acid and water to the titanium
alkoxide determine the formation of the final product, be it a gel,
solution, or colloid. The reaction of titanium alkoxides with
carboxylic acids is illustrated in Figure 3. The acid reaction allows
the replacement of one or more of the OR functional groups attached

0 0
II II
nRCOH + Ti(OR')4—> (RCO)nTi(OR')4_n+ nR’OH

Figure 3 Titanium alkoxide/carboxylic acid reaction.

 

 

M(0R) 4 dissolved in alcohol

 

 

 

 

 

dissolved in alcohol

 

 

I

 

clear solution

 

J

 

 

pol gme ric sol

 

 

'F—j

dipping

 

I

 

 

supported membrane

added at 25°C with
high speed stirring ,
small quantity of water

 

 

 

gelling

controlled
rel humidity

 

 

 

clear supported
gel membrane

 

 

 

fi ri ng

400-50006

 

 

 

ceramic membrane

 

 

 

l

 

 

pouring

H

_

 

 

water

 

I

 

hydroxide precipitation

 

J

 

suspension

1’—

 

12 hours Jheating 85-9500

 

colloidal suspension

 

cool to room J temperature

 

stable colloidal sol

 

 

 

HN03

 

 

 

 

sol in plastic container

 

 

 

control led

 

gelling

 

transparent unsupported

 

 

membrane

 

Figure 2 Sol-gel products flowchart.

rel humiditg

 

8
to the titanium with the corresponding carboxylic acid groups. This
acid reaction may affect the kinetics and yield of the condensation
and hydrolysis reactions by steric hindrance. The hydrolysis and
condensation reactions cause the titanium alkoxide to polymerize
into linear, and possibly branched structures. The generic hydrolysis
and condensation reactions are shown in Figure 4. The condensation
reactions occur in the last two steps of this equation. The

 

-ROH . (RO)Ti(OR)3 . .
(RO)3TiOR + H20 -—>(RO)3TIOH ROH > (RO)3TIOTI(OR)3
H20
(RO)3TiOTi(OR)2OTi(OR)3

Figure 4 Hydrolysis and condensation reaction
of titanium alkoxide.

combination of these two reactions allows the formation of a
organometallic backbone with attached organic groups that is

suitable for film coatings. Yoldas17 states that:
"This is done first by controlling the amount of water and
dilution of the system, and second, by the presence of a
critical amount of certain acids...solutions are useful in
depositing optical titania coatings..."

Therefore, the reactions represented in Figure 3 and 4, when used
with the appropriate amounts of water and organic acids, should
allow the synthesis of a solution that can be used to coat a
substrate with an optically transparent film.

2.3 Indicator Chemicals

Use of a film that incorporates a metal ion suggests that a
metal-ligand reaction may occur. Textbooks, including Masterton18,
indicate that metal-ligand species generally show intense colors.
Ligands are, in principal, any molecule or anion with an unshared
pair of electrons, such as, NH3, H20, OH', and Cl“. Kirk-Othmer16

states in Encyclopedia of Qhomical Technology that:

9

"Phenols react readily with TPT(tetraisopropoxytitanium) and
the equilibrium lies far to the right, especially with diphenols,
such as substituted catechol and...products are yellow or
orange."

This suggests that a bidentate ligand, such as catechol or pyrogallol,
may react with the titanium-based film giving rise to a color
change. These bidentate ligands have hydroxyl functional groups
that reacts with the titanium similar to the diphenols discussed by
Kirk-OthmerlG. The mechanism of this titanium to indicator
reaction and color change is not well understood since the
composition and structure of the film has not been determined.
Cotton19 and Pierpontz0 discuss the possible binding of catecholates
to metal complexes. These authors believe that both OH groups of
the catecholate bind or complex to the metal atom in the
organometallic complex. Determination of possible indicator
chemicals is now a matter of searching through various catalogs and
references including: Aldrich21, Sigma”, and the Merck Index”.
These possible indicator chemicals should have two functional
groups consisting of unshaired electrons, should be non-toxic and
stable, and should be inexpensive.

2.4 Solvents

Solvents required for this project must dissolve the indicator
chemical in sufficient amounts to allow reactions to occur with the
film. These same solvents should not degrade or react with the film.
The solvents should also be non-toxic and have a low vapor pressure
with specific melting points appropriate to the desired temperature
range. The melting point of the solvent will determine the
temperature at which the reaction between the indicator and the
film will begin. Catalogs and references such as Aldrich21,
Sigmazz, and the Merck lndex23, can be used to select possible
solvents on the basis of melting point and reactivities. Trial and
error experimentation with the indicator and film would most likely
be the only method of determining if these solvents are acceptable
for a time-temperature sensor.

3. MATERIALS

3.1 Films

Our research group has been primarily concerned with the use
of two different substrate films. The two films are based on
titanium tetra-isopropoxide, water, and either valeric or valeric and
lauric acids combined. The films produced are optically clear,
scratch resistant, and stable. The films can be easily spin-cast onto
a glass or other type of substrate by the use of a tabletop
centrifuge.

During the course of this study, preparation methods for the
films were changed as a result of new information supplied by
Beatrice Torgerson during internal lab discussions. This new method
of film preparation was introduced at the same time that our
emphasis switched from the cold temperature to the high
temperature indicator studies when it became apparent that the low
temperature sensor could not be quenched. The low temperature
(-20°C to 30°C), original film preparation materials and
concentrations are illustrated in Table 1 on the next page. The two
major film types are based on valeric or lauric/valeric acids
combined with titanium tetra-isopropoxide and water. All
chemicals were supplied by Aldrich and used without further
purification. The water is deionized by reverse osmosis(RO) to 18
M!) x cm resistivity. The film components are combined in the top-
down order given by the‘table with sufficient mixing by vortex
stirrer to ensure a homogeneous solution. Mixing of the solution
should occur between all additions of chemicals. The final solution
can then be applied to the substrate.

IO

l 1

Table 1 Original film composition.

 

 

 

 

 

 

Valeric Acid Based Lauric/Valeric Acid
Based
S cies Amount mam —-iElE-l
Valeric Acid ‘ 1.65 ml 9.03 2.50 ml 6.84 l
Lauric Acid 0.0 g 0 250 mg 0.37 '
Titanium lsopropoxide 0.5 ml NA H 1.0 mi NA
no Water 46 LII 1.52 |] 46 in 1.52 _J|

 

 

 

 

The ratios are included in Table 1 since the sol-gel field of
chemistry routinely uses this type of nomenclature. All ratios are
compared to titanium tetra-isopropoxide on a molar basis. The acid
ratios to titanium are normally given the symbol Ra while the water
ratio with respect to titanium is given the symbol Rw.

The incorporation of the lauric/valeric based films resulted
from experiments performed by Beatrice Torgerson. It was
discovered that stearic acid, a possible indicator solvent (see
section 3.3), caused the valeric acid based film to dissolve.
Therefore, the lauric/valeric based film was included as a possible
alternative that may resist degradation in a stearic acid solvent
environment.

High temperature (greater than 60°C) studies incorporated the
new film preparation techniques determined by Torgerson, Dunuwila,
and Berglund24. They determined that the Raman spectra for the
film solutions did not change appreciably when the R3 was between
six and nine. Joel Dulebohn had also performed experiments with
these film preparations with good results as discussed in available
internal lab notes. Since this new film preparation produced stable
and homogeneous films and had been used successfully before, this
method was adopted. The preparation and concentrations of the new
films are shown in Table 2. The preparation of the lauric/valeric

1 2
acid based film begins with the mixture of both acids. Once the
lauric acid has dissolved in the valeric acid, titanium tetra-
isopropoxide is added and stirred on a vortex mixer. This solution is
allowed to react for at least 6 hours in the dark. Lastly, the RO
water is added and again agitated on the vortex mixer. This final
solution is placed in dark storage for at least 12 hours before being
applied to the glass substrate. The valeric based film is prepared
identically without the addition of the lauric acid.

Table 2 Current film composition.

 

Valeric Acid Based I L—"ric/Valeric Acd
_______________,__w_. .

Species Amount Ratio Amount

 

 

 

 

 

 

 

 

Ratio I
Valerie Acid ]| 2.7 mi 7.39 2.55 mi 6.98 l
Lauric Acid ][ 0.0 g 0 250 mg 0.37 1
Titanium Isopropoxidell 1.0 ml NA 1.0 ml NA l
RO Water 88 iii 1.46 88 iii 1.46 l

Zirconium based films were also prepared to determine if a
non-reacting zirconium film layer would affect the time-
temperature color change reaction. The composition of the
zirconium based solution is given in Table 3.

Table 3 Zirconium film composition.

 

 

 

 

 

 

 

S ecies Amount Ratio
IVaieric Acid I 1.7 ml 7.
|| Lauric Acid ]l 250 mg 0.55
IIZirconium n-Propoxide ll 1 ml (70 wt.%) NA
IIRO Water || 60 ul _ 1.49

 

l 3
The zirconium propoxide was obtained from Aldrich and used without
further purification. This zirconium film solution was prepared
using the same techniques as the lauric/valeric film new
preparation discussed above.

All film solutions can be applied to a glass substrate using a
sample spinning method. A disposable glass Pasteur pipette (VWR
cat. no. 14673-043) was used to spread the required amount of
solution onto the substrate. Enough solution should be applied so
that during sample spinning, the solution should be spread uniformly
over the substrate. Sample spinning should occur for at least 5
minutes. A shorter spinning time, 1 minute, can be used if the
film/substrate is then allowed to dry overnight in a dark, clean
environment. The zirconium based solution can be applied over
previous film layers by the same method. Our studies used an
International Clinical Centrifuge with the glass substrate centered
and affixed to the hub of the rotor with double sided tape and
oriented horizontally. The substrate used was pre-cleaned
microscope slides from Erie Scientific (No. 2954-F) cut into strips
insertable into the spectrophotometer cuvette. These slides were
approximately 1x2.5 cm in size and required approximately 2 drops
of solution. Spinning of these precursor solutions result in a
uniform film layer of approximately 3000A in thickness. This film
thickness was determined using profilometry studies on the films
performed by Joel Dulebohn during the course of his research and
discussed in internal lab notes.

Films can also be calcined by heating in an oven set at 400°C
or more for approximately 8 hours. This heating appears to convert
the film into a ceramic membrane as shown by the flowchart in
Figure 2 contained in section 2.2. Preliminary tests of calcined
films indicate that no reactions occur with indicator chemicals.

1 4

3.2 Indicator Chemicals
3.2.1 Low Temperature

Kirk and Othmer16 state that "Phenols react rapidly with
TPT(tetraisopropoxytitanium)...products are yellow or orange."
Phenols are hydroxy substituted benzene rings. Barrow25 discusses
that colored compounds often involve aromatic rings. Combining
these two statements indicate that possible indicator chemicals
would consist of an aromatic ring with attached hydroxy groups.
Cotton and Wilkinson19 state that catecholates are known to react
with metals in solution. These known solution reactions with this
type of chemicals will hopefully work similarly in the solid film
system that we are trying to develop.

The actual mechanism of the indicator to metal reaction is
unknown since the film has not been completely characterized to
this date. As discussed in section 2.3, it is believed that both OH
groups bind to the metal. It is unknown whether the indicator OH
group displaces a titanium-organic bond or if the indicator OH group
changes the coordination number of the titanium. Since we believe
that the film is stable in normal conditions and solvents, this would
lead us to believe that the indicator changes the coordination
number of the metal, although, this has not been proven. Since the
film shows no signs of degradation after the addition of the
indicator, we believe that the titanium coordination is changed from
four to six with the addition of a catecholate indicator.

Chemicals containing an OH functionality tested for the low
temperature sensor include: pyrocatechol, pyrogallol, phenol, P-
chlorophenol, 1-napthol, P-nitrophenol, anisole, benzoic acid, sodium
benzoate, P-benzoquinone, 2,4-dichlorophenol, tetrachlorocatechol,
pentachlorophenol, and alizarin. The chemical structure of these
molecules, among others, is included in Figure 5 on the following
pages.

15

O 0

2EDTA

CH3 —c—o-CH2 -c-o — CH3
ACAC

fl. 1:

Pthalic Anhydride

 

OH 1 ,-10 Phenanthroline

 

C(CH3)3

Alizarln 0“ 0
OH
OH O 0
OH OH
. CH
l l .3
ESCU etn Orcmol Monohydrate
o 0 OH
*0 C1 00C
Cl
0 OH

6,7-Dichloro-1,4-dihydroxy-

P-Benzoquinone .
anthraqumone

Figure 5 Chemical structure of indicators.

16

0
OH Cl 0
01’ H ‘OH

0 OH 0

2,5-Dichloro-3,6-dihydroxy Jug|one
-p- benzoquinone

OCHs
O OH OCH:
Lawsone O
0 Veratrole
o

0 CI 0
o
00 , ,
1,2-Naphthoquinone Cl
Tetrachloro-1,2-benzoquinone

 

C(CH )3 OH C(CH3)3
OH O l
Galangin CH3
CHZOH BHT
COOH

HCOH
O o
_ OH
OH

OH OH . . .
3,4 Dh dro Ben oc Acd
Ascorbic Acid ' y xy 7' ' '

Figure 5 (cont'd)

17

COOH OH

I i OH
OH OH OH

3,5 Dihydroxy Benzoic Acid Pyrogallol

on

OH OH
(Ff 1 OH
H3 Catechol

4-Methyl Catechol

OH
COOH OH
OH
CH3

Salicylic Acid 3-Methyl Catechol

OH

C] 0” 01H OH

Cl 5-Chlorocatechol
Tetrachlorocatechol

OH OH C1
: ,OH Q
C C

l
l .
4-Cholrocatechol 2,4-chhlorocatechol

FiQure 5 (cont'd)

18

OH
OH OH
/ \
CH3/ EH3 CH3 CH3 NO2
3,5-Di—t-butylcatechol P'N'tmphenm
OH O/CHS
1-Napthol Anisole
OOCHQCHZCHg OH
OH OH OH
Resorcinol

on
N-Propyl Gallate

COONa OH

OH
I I CH3
0/

Sodium Benzoate 3—Methoxycatechol

COOH 0“
Benzoic Acid Phenol

Figure 5 (cont'd)

1 9

3.2.2 Elevated Temperature

The possible indicators that were selected for trials for the
high temperature region were chosen from the chemicals available
in our lab that had a OH functional group. Catechol type chemicals
with a hydroxy functionality were selected for testing as discussed
in section 2.3 and 3.2.1. Chelating chemicals were also tried since
these agents (EDTA, acac, and others) often produce colored
reactions with metals. Natural products (BHA, BHT, and flavones)
that would be acceptable to the food industry were an additional
group that was qualitatively studied. The structure of all these
possible indicators, among the low temperature indicators, tested is
shown in Figure 5 found in the previous section. Again, as discussed
in section 3.2.1, any indicator chemical should react with the
titanium incorporated in the film and give a visible color change
within a reasonable amount of time without degradation of the film.

3.3 Solvents

The choice of solvents for the indicator chemical is
determined by the temperature threshold required for the sensor.
At the melting point of the solvent, the dissolved chemical and cast
film will begin to react giving rise to a color change. A partial list
of possible solvents is given in Table 4 on the following page. It
was discovered that stearic acid dissolved the valeric based films
as discussed in section 3.1. We also determined that the
lauric/valeric based film would degrade in stearic acid. This
degradation of the films suggested a shift in emphasis from the
acids to the use of waxes as solvents for the indicator chemicals in
the high temperature regime. Commercial candle paraffin wax
(Gulf@ wax) with a melting range of 51°C to 53°C was successfully
utilized. Moreover, in order to meet a variety of temperature
thresholds for the sensor, wax blends were graciously provided by
IRM (Industrial Raw Materials). Namely, IRM #8618 and Hewax with
melting points of 80-84°C and 110-118°C respectively, were
investigated. Other solvents may be acceptable if they are
transparent to the wavelengths of light detected, dissolve sufficient

20

Table 4 Solvents and their melting points.

 

Solvent Meltin. Point, 00

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Diethyl Succinate ' - 2 0
Diethyl Maleate -1 0
IrDiethyl Fumarate 1 - 2
lMonoethyl Succinate 8
Dimethyl Succinate 1 9
|| Lauric Acid 4 4 - 4 6
lf Paraffin Wax 51 -53 1'
I[ Stearic Acid 6 7 - 6 9
IRM #8618 Wax 80-84
FMalic Acid 101 -1 03
IRM Hewax 110-118
|DL Malic Acid 131-133

quantities of indicator chemicals, and do not react with the film or
substrate. The solvents we primarily used during the course of this
study were diethyl fumarate, dimethyl succinate for the low
temperature studies, and the 3 waxes listed in Table 4 for the work
at elevated temperatures. The melting points of these solvents
were determined from the Merck Index21 and through Industrial Raw
Materials(lRM) Corporation representatives for the wax blends.

It is important to mention that for a practical application, it
might be necessary to use multiple sensor strips with different
solvents in order to obtain more precise information on the time-
temperature history of the environment. As the lowest melting
point temperature is reached, an imbedded film sensor will begin to
react. When the next lowest temperature is obtained, the second
film sensor will proceed with the color change reaction. The time
between the lowest and next lowest melting point temperature will
be indicated by the increased intensity of the color of the first film
compared to the second film and taking into account the change in
reaction rates as a function of temperature.

4. RESULTS

4.1 Low Temperature Sensor
4.1.1 Construction and Materials

The construction of a cold temperature (-20°C to 30°C) sensor
involved first determining the appropriate materials. The valeric
acid based film (original preparation) was chosen for ease of
synthesis. Diethyl fumarate was also chosen as the solvent since
the melting point is approximately 0°C which would be important in
the frozen food storage industry.

The indicator chemical for the cold temperature sensor was
chosen from the chemicals discussed in section 3.2.1 and illustrated
in Figure 5. Low concentrations of possible indicator chemicals
were dissolved in diethyl fumarate and allowed to react with the
valeric acid based film coated glass slide for long periods of time.
Visual inspection for a color change of these films over time
indicated if the chemical was an acceptable indicator. Other
phenomena that would affect the sensor performance, such as
solution color changes or film degradation, were also noted. In all
cases, the reaction was studied at 32°C. The compounds that were
most effective in producing a color change in the film were
pyrocatechol, commonly known as catechol, and pyrogallol. P-
nitrophenol and 1-napthol also gave reasonable color changes. The
intense color changes and long reaction times that occur with such
low concentrations indicate that these chemicals may be very
efficient indicators in the low temperature region.

Further optimization of the low temperature indicator
chemical was performed with catechol and pyrogallol. A kinetic
curve was constructed from reactions of these two chemicals in
diethyl fumarate at 32°C. This curve is shown in Figure 6.

21

1.4

 

1.2~

0.8- .. '

o.6~

Relative Absorbance

El 288 ppm Pu rogallol
1 O 209 ppm Catechol

 

 

 

I I
500 1000 l 500

Time (Min)
Figure 6 Absorbance as a function of time for pyrogallol

and catechol in diethyl fumarate reacted with
titanium based film at 32°C.

23

The relative absorbance reading was determined by the difference in
intensities between the baseline, 700 nm, and a location on the peak
maximum that corresponded to 440 nm for catechol and 450 nm for
pyrogallol. Of these two indicators, catechol was chosen as the
optimal low temperature indicator since catechol gave a more
intense absorbance reading.

Various methods were attempted at forming a self-contained
sensor. One method attempted was to spray a fine mist of catechol-
containing dimethyl succinate to a glass slide that had been cooled
to approximately -195°C by immersion in liquid nitrogen. This
method displayed an intense color change after storage for 4 days in
a freezer at -18°C. Mist spraying of pure dimethyl succinate onto a
liquid nitrogen cooled slide followed by a mist spraying of catechol
in dimethyl succinate also displayed a color change after 4 days
storage in a freezer. This color change occurred In patches
indicating a non-homogeneous covering. The most successful method
resulted in immersing a liquid nitrogen temperature film into the
pure solvent followed by a misting of the catechol/dimethyl
succinate solution. This increased thickness of the pure solvent
caused by the dipping prevents the indicator chemical from reacting
with the film. Dimethyl succinate was chosen for these tests since
it has the highest melting point of the cold temperature solvents,
and therefore, is easiest to study. The use of sprays and immersions
to coat the slide caused the frozen solvent to render the sensor
opaque to the Perkin Elmer Lambda 3A UV/Vis spectrophotometer.
Therefore, it was necessary to determine a method of removing the
opaque solvent layer to allow a UV/Vis spectrophotometer
measurement of the film.

4.1.2 Cleaning and Quenching

Attempts to clean the film surface included physical wiping,
rinsing with R0 water, and rinsing with 50% by volume ethanol and
water. Studies were done with both frozen slides and slides above
the melting point of the diethyl fumarate (1-2°C) solvent. The

24
slides were allowed to react for approximately 30 minutes to
produce a visible color change. One half of the slides were frozen
and cleaned. The other one half were immediately cleaned of the
liquid solvent. Additionally, two slides were kept without cleaning
for a reference. Cleaning of the frozen slides was accomplished by
first knocking the frozen solvent layer off of the slide followed by
cleaning by wiping with a Kimwipe@, rinsing with R0 water, or
rinsing with 50°/o(vol.) ethanol and R0 water. The films in the liquid
solvent were also cleaned by these methods. Results show that any
rinsing of the slide causes a loss of intensity by up to 50% compared
to measurements obtained before rinsing. This loss of intensity may
be caused by the replacement of the catechol that is attached to the
titanium by water or ethanol since all of these species have an OH
functionality. Use of other cleaning solvents without an OH group
may not affect the intensity of the color change, but were not
pursued due to the problems encountered in the quenching
experiments discussed below. The cleaned sensors were monitored
over 3 days. The intensities did not vary more than a few percent
over this time indicating that the reaction may be quenched if
cleaning of the slide is successfully performed. This implies that
the sensor will be relatively stable after cleaning is performed.

Quenching studies were made using 98 ppm catechol in
dimethyl succinate. The solvent was sprayed onto a liquid nitrogen
cooled unreacted film and placed in a refrigerated water/ethylene
glycol bath at -28°C for one day. The edges of the slides, after
cleaning, showed a color change visible to the naked eye. The center
of the films gave an absorbance reading of approximately 0.08. The
appearance of a color that occurs on an unreacted film indicates that
diffusion still occurs when the solvent is frozen and that the
reaction will not quench even at temperatures approximately 50°C
below the solvent's melting point. Therefore, a sensor of this type
will not stay inactive and will not quench when returned to
temperatures below the freezing point of the solvent.

25
4.1.3 Results and Discussion
Since the quenching studies indicated that the reaction
proceeds after refreezing, it was decided to determine if this
technique would work for high temperatures(65°C to 140°C).
Therefore, only a few studies were conducted with the cold
temperature sensor.

Experiments were performed to determine the reproducibility
of the cold temperature sensors. Films were allowed to react for 30
minutes in 98 ppm catechol/dimethyl succinate solution at 30°C.
The films were then frozen at a freezer temperature of -18°C for
five hours. The slides were cleaned by physical removal of the
frozen solvent and intensities measured. Results indicated
reproducibility of the color intensities within 15% of the average.

Results of experiments to determine change in intensity as a
function of concentration were carried out in two different solvents.
Concentrations of catechol from 1 to 1000 ppm were studied in
dimethyl succinate and diethyl fumarate at 32°C for approximately 3
days. Results of these experiments are shown in Figure 7 for
dimethyl succinate and Figure 8, on the following page, for diethyl
fumarate. The line fitting of these data points is by computer
interpolation. The absorbance readings consist of the intensity at
440nm minus the background intensity at 620nm. Concentrations of
catechol in dimethyl succinate lower than 10ppm could not be
studied since the resulting intensity was less than 0.1 absorbance
units. The results displayed in Figures 7 and 8, on the following
pages, indicate that different concentrations of catechol will give
different intensities as a function of time and may be used to
customize sensors for specific applications.

 

 

 

 

0.5
II
fl
0.4-1 I
cu I ’
o
5
I
‘e 0.3-1 0
o O
U) o
.0
<2 . a
g’ 0.2
1'5 ' E,
'33 a
0‘ 0.1 an I 1031 ppm
0 103ppm
B 10.3ppm
0.01 r , . f f 1
O ' 1000 2000 3000
Time (Min)

Figure 7 Relative absorbance-time profile of
catechol/dimethyl succinate solution reacted with the titanium
film at 32°C.

 

 

 

 

1.0
o
0.84 °° ° °
0) ° .
2 .. . '
g I o 981 ppm
§ 0'63 I I 981mm
.0 O 9.8ppm
< ‘9. a 10ppm
0.) .
.2 0.4--
6 O . O
'5
01 o
0.2 .0 a E, a
one
0.0 . , . , . ,
0 1000 2000 3000
Time (Min)

Figure 8 Relative absorbance-time profile of
catechol/dimethyl fumarate solution reacted with the
titanium film at 32°C.

28

To summarize the results of the cold temperature sensor, the
construction materials were; catechol as the indicator and valeric
acid based original preparation for the film. This resulting cold
temperature sensor does not quench efficiently when returned to
temperatures below the freezing point of the solvent. The
absorbance intensity varies as a function of concentration and time
as expected. The sensor requires a thick layer of frozen pure solvent
followed by a misted layer of solvent and indicator chemical to
prevent premature reaction. Therefore, the use of such devices
would be appropriate only to indicate whether a particular
temperature threshold was reached. Once this temperature
threshold is reached, a visible reaction is quickly apparent. This
reaction occurs rapidly due to the fast melting of the thin layer of
solvent allowing almost immediate reaction between the indicator
chemical and the film layer. However, the length of exposure could
not be reliably determined since the reaction proceeds beyond
refreezing. For this reason, no further kinetic analysis was
performed on the cold temperature system.

4.2 Elevated Temperature Sensor
4.2.1 Construction and Materials

The construction of an elevated temperature range (65°C to
140°C) sensor, like the cold temperature range sensor, involved first
determining the appropriate materials. This section of research was
conducted after new film preparation techniques were developed by
Torgerson as discussed in section 3.1, and therefore, the
investigation was pursued utilizing these new films. Most of the
chemicals listed in Figure 5 were allowed to react with both the
valeric and valeric/lauric based films at 65°C for up to five hours.
The solvent used for these studies was 1ml of paraffin (Gulf®) wax
containing 0.5M to 1M of the indicator chemicals. This study
indicated that the valeric/lauric based film produced intensities
equal to, or greater than, the valeric based film. Therefore, we
determined that the valeric/lauric based film (new preparation)
would be used for the remainder of this study. All thermal reactions

29
for the elevated temperature sensor were carried out in a Fisher
Scientific Isotemp® Programmable Oven (Model 818F).

Continuing with the determination of the materials,
qualitative measurements of the potential indicator chemicals was
performed as described in the previous paragraph. Visual results
including the solubilities, solution and film color changes are
tabulated in Table 5. The goal of this qualitative research was to
find an indicator that would react with the titanium to give an
obvious color change within a reasonable amount of time as
discussed in section 3.2. These results show that the most likely
high temperature indicator would be found from the catechol-like
compounds. These compounds are colorless in solution and react
well with the film producing a color change.

The most successful chemicals of the qualitative studies
shown in Table 5 were used for a more quantitative experiment to
determine the most suitable chemical to use with this high
temperature (65°C to 140°C) film. Some additional chemicals not
listed in Table 5 were also included in this study. These additional
chemicals were included based on the similarities between these
chemicals and the most qualitatively effective chemicals, the
catecholates. These additional chemicals are illustrated in Figure 5.
This quantitative study was done by evaluating the reaction
intensity, reaction kinetics, and the quenching performance of the
colorimetric reaction. The compounds were dissolved in
approximately 2ml of melted paraffin wax at a temperature of 65°C.
Excess indicator was added to the melted wax and allowed to sit
overnight at 65°C to ensure saturation and equilibrium.
Valerie/lauric acid based film coated slides were immersed in the
65°C wax solutions for periods of 5, 10, 15, 30, 45, and 60 minutes.
The wax solutions were placed in a water bath at 65°C to ensure
thermal stability. Films removed from the wax solution were hand
shaken to remove the excess wax from the slide. Absorbance of the

Table 5 Qualitative determination of indicator chemicals for the
high temperature sensor.

Titanium film reaction in paraffin wax at 65°C for five hours

 

 

Solution
Color

Solubilit
in Wax

 

ll Chemical Name
TA

 
  
 

Reachon
Color

 
  
   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

none "aprox. 1/2' none
If, yellow 2-phases none
1,10 Phenanthroline none partly none
onohflrate
Pthalic Anhydride none partly none
IBHA rusty-red partly rusty-red
Elizarin yellow/ partly rusty red
orange
hrysin pale yellow partly pale yellow
IlEsculetin pale yellow partly none
IIOrcinol Monohydrate mle yellow mostly yellow
IlP-Benzoquinone yellow partly yellow
,7-Dichloro-1,4- cloudy rusty partly light purple
ihydroxylanthraquinone color
,5-Dichloro-3,6-dihydroxy-p- red/orange partly red-purple
nzoqumone
uglone yellow/ partly slight red
orange
Lawsone pale yellow partly pale yellow
"Veratrole none 2 phases none
Iflz-Naphthoquinone dark slightly none
etrachloro-1,2-benzoquinone red/orange partly yellow
alanflqin pale yellow slightly yellow
HT none partly faint yellow
scorbic ACld none partly light yellow
,4 Dihydroxy Benzoic Acid none partly faint yellow
,5 Dihydroxy Benzoic Acid none partly faint yellow
none partly yellow
none partly dark
brown/red
none partly dark yellow
none artl ale ellow

 

 

 

 

 

 

3 1
film from 700 nm to 350 nm was recorded on the Perkin Elmer
Lambda 3A UV/Vis Spectrophotometer in a polystyrene cuvette
versus a blank film in a polystyrene cuvette. The difference in
absorbance from 350 nm to 600 nm was calculated from the
graphical output of the spectrophotometer.

Kinetics of reactions with the film were followed by
determining the absorbance of one film that had been immersed in
the wax solution for 5, 10, 15, 30, 45, and 60 minutes. Kinetic
curves of absorbance versus time were plotted and used to give a
qualitative estimate of the chemicals kinetic feasibility. An
example of this type of plot is given in Figure 9. If the kinetic
curve, plotted in this manner, had a smooth shape with the reaction
taking at least 10 minutes before reaching a plateau, that chemical
was determined to have good kinetic possibilities for further study.
Chemicals that did not have this type of kinetic curve were
categorized as poor.

The intensity of the reaction between the chemical and the
film is the second criteria we used to determine the adequacy of the
chemical. The difference in absorbance from 350 nm to 600 nm
after 60 minutes of reaction is the basis for the intensity
measurement. Relative intensities greater than 2.0 are categorized
as high, and intensities less than 0.2 are categorized as low with
other classifications distributed throughout the remainder of the
range.

Quenching studies of the chemicals were done by reacting the
films for 5, 10, 15, 30, and 60 minutes in the saturated wax solution
and obtaining a baseline absorbance. The films' absorbances were
then determined approximately five hours later and then again after
24 hours. The films were stored in the dark between readings. The
change in absorbance compared to the baseline is the basis for the
quenching evaluation. A good quenching classification resulted if
the absorbance intensity did not vary more than approximately 10%

 

 

 

 

1.0
la

0.9 — °
m B
8 I a
O
E
o 0.6 ~ 0
U)
1:)
<1:
0)
.3. 0.4 e a
o-I
O
a) 4
C!

0.2 ~

0 0 {Fr f T fi T r

0 20 40 60

Time (Min)

Figure 9 Kinetic results of catechol/paraffin wax solution
reacted with titanium based film at 65°C.

33
absorbance over the initial value for a majority of the film samples.
Other classifications were more arbitrary and were based on the
changes in intensity after 24 hours compared to the baseline.

The results of the kinetic, intensity, and quenching feasibility
studies on various chemicals are given in Table 6. Again, the
chemical structure of these chemicals is illustrated in Figure 5.
Some chemicals, like catechol, pyrogallol, and phenol were also
studied in section 4.2.1. These compounds were repeated to
determine if increased temperature would make these chemicals
more suitable for indicators. Using the results in Table 6 it was
decided that the chemicals for further study for the high
temperature sensor would be: 4-methyl catechol, catechol, and
methoxy catechol. All have good kinetic and intensity
classifications with fair quenching results. It was decided

Table 6 Feasibility of indicator chemicals
for high temperature sensors.

Chemical Kinetics lntensit
N-Pro l allate Iow
3-Meth l catechol r r
4-Met Icatechol
BHA
Tetracloro catechol

Phenol
3,5 Di-t-Butyl fair-good
catechol
Resorcinol

echol fair
Metho catechol fair

 

that quenching was less important than kinetics and intensity since
it is not likely that long delays would occur between the color
change reaction and the measurement of these high temperature
sensors. However, it was also decided that methoxy catechol has an

34
intensity that is too large(>2.00) for our purposes. This high
intensity indicated that kinetic studies for times greater than 60
minutes would exceed the maximum instrument reliability of 3.00
absorbance units. Catechol was the chemical of choice for the high
temperature sensor since it is readily available, inexpensive, and
worked well in the low temperature studies. 4-methyl catechol may
be a suitable chemical for temperature ranges greater than 150°C
since it has a greater melting point than catechol.

The wax blends listed in Table 4 were chosen as the solvents
for the high temperature sensor. These specific waxes are paraffin
wax, IRM Hewax, and IRM #8618 wax. Qualitative tests of the
solubilities of indicator chemicals in the wax blends indicated that
sufficient amounts of indicator would dissolve in the wax to give a
color change to the film. Therefore, since waxes are easy to work
with and non-toxic, these wax blends were chosen as the solvent
medium for the higher temperature sensor.

4.2.2 Cleaning and Quenching

Attempts were made to determine a method of removing the
wax solvent layer from the high temperature sensor. This removal
of the wax layer was desired to allow easier visual and UV-Vis
Spectrophotometric analysis of the sensor. Rinsing with boiling
water, wiping with a Kimwipe®, and freezing (10°C) the vial
containing the wax and slide were methods attempted. Rinsing
and/0r wiping the slide caused a reduction of the color intensity.
Freezing 0f the wax and physical removal of the slide was very
difficult due to the breakage of the slide from the force required to
remove the slide from the frozen wax containing vial.

Due to the problems encountered in removing the wax from the
slides, the slides were cleaned upon removal from the indicator
solution by vigorous shaking of the slide. When measurements were
required, the slide was removed from the melted wax solution and
physically shaken to remove most of the excess wax. Applying the
bottom edge of the slide to an absorbent material such as a paper

35
towel, assisted in the removal of the excess wax by capillary action.
This method of cleaning was tested by briefly immersing previously
reacted slides in a pure wax solution to build up thicker and thicker
layers of wax, a method similar to candle making. Measurements of
the background (600nm) and the colored band (350nm) were obtained
after each successive wax coating. The relative color intensity did
not appreciably vary until the third or fourth layer of wax was
applied. Three or four wax layers produced a relatively thick wax
coating compared to the wax thickness on the slides that resulted
from the method of physical shaking discussed earlier. Therefore, it
was concluded that this method of cleaning the slides, physical
shaking, would be effective and allow easier visual and UV/Vis
spectrophotometer measurements.

The quenching of the high temperature sensor was discussed in
section 4.2.1. Since catechol was the indicator chemical used for
this study, and based on data discussed in section 4.2.1, it appears
that once the wax solution solidifies, the colorimetric reaction rate
approaches zero and quenching of the sensor occurs.

4.2.3 Results and Discussion

Two brief variations on the construction of a high temperature
sensor were attempted. The first was the addition of a zirconium
film layer on top of the titanium film layer. It was believed that a
layer of zirconium based film would provide a diffusion barrier to
the indicator, thus allowing a longer reaction time. Also, it was
determined that zirconium films do not react with catechol as does
titanium films. A coating of the zirconium film solution was placed
over a valeric/lauric new preparation film. These two layer films
were reacted for one hour in four different indicator chemicals of
approximately 0.5M concentration that were dissolved in paraffin
wax at 65°C. Comparisons were made of the zirconium coated
sensors to valeric/lauric film sensors. Visual observation of these
sensors indicated that the films with an extra coating of zirconium
produced slightly darker color changes in reactions with catechol
and 4-methyl catechol solutions. This indicates that the reaction

36
rates are increased with the addition of a zirconium film layer.
Reactions with orcinol and salicyclic acid solutions did not produce
any appreciable change in intensity.

An additional experiment was performed using basic (pH>7)
solvent solutions and basic film preparation solutions. This
experiment was performed to determine if pH would affect the
colorimetric reaction in the hope that the color would shift from
yellow to a more visible color such as red. Reactions were carried
out on valeric/lauric films reacting with 0.119 catechol dissolved in
1ml of paraffin wax. The wax solution was made basic with the
addition of NaOH pellet of approximately 0.089. These reaCtions
produced a more intense color change when compared to a neutral
solution. The excess non-dissolved catechol becomes green-black
colored on contact with the NaOH indicating possible degradation of
the catechol. Film solutions with a pH greater than 7 were prepared
by using a valeric based film solution with approximately 0.089 of
NaOH added after addition of the water. The films prepared by this
method did not produce a homogeneous covering when spin-casting
was attempted. Films prepared from this solution were reacted
with four indicator chemicals in paraffin wax at 65°C for 5 hours.
4-methyl catechol and catechol indicators produced a non-
homogeneous color change (dark red/brown and yellow/orange,
respectively). Reactions with salicylic acid and 6,7-dichloro-1,4-
dihydroxy anthraquinone produced more uniform colors of yellow and
light purple, respectively. These experiments were not pursued
since an increase in color intensity would cause a corresponding
decrease in reaction time and the measuring lifetime of the sensor.

Kinetic studies were performed on the three wax blends at
various temperatures above their melting points. Catechol was
added to'the melted waxes in excess and allowed to equilibrate
overnight. Initial experiments with paraffin wax used the
supernatant as the solution and are described as unsaturated
experiments. Later experiments used the catechol-wax solution
supernatant with the addition of a few crystals of catechol to

37
ensure the constant concentration of the solution during the kinetic
run and are labeled as saturated solutions. The temperatures
studied were: 65, 85, and 95°C for paraffin wax (melting range 51-
5300); 90, 100, 110, and 120°C for the IRM #8618 wax (melting
range of 80-84°C); 120 and 130°C for the IRM Hewax (melting range
of 110-118°C). The reactions were monitored for up to 5 hours with
measurements generally taken at 5, 10, 15, 30, 45, 60, 150, 240, and
300 minutes after the reaction was initiated. The reaction was
initiated by the addition of a film-covered glass slide to the vials
containing the catechol/wax solution at the desired reaction
temperature. Two types of blank slides were also measured for all
time and temperatures. These blanks consisted of film coated slides
immersed in pure wax solutions, and also as clean slides immersed
in the catechol-wax solution. An example of the data collected for
one sample at one temperature at a specific time is shown in Figure
10 on the following page.

An example of the completed data generated by these
experiments is shown in Figure 11, two pages following. This is a
plot of the relative absorbance of the colored film product of the
IRM#8618 wax/catechol solution reacted at 100°C averaged over all
of the experimental runs. The relative absorbance is the difference
between the absorbance intensity at 350nm (colored region) from
the intensity at 600nm (background region) as measured by the
Perkin-Elmer lambda 3A UV/Vis spectrophotometer. Calculation of
absorbance using relative values is required to eliminate the errors
that may result from measuring the intensity through a variable
thickness of the solidified wax solution.

Analysis of the data generated by these experiments was
attempted using various models. This analysis was desired in the
hope that useful calibration curves suitable for industrial
application would be found. This data reduction was also used to
attempt to eliminate and reduce the inherent errors and scatter of
using a UV/Vis spectrophotometer (designed for solutions) on solid
wax covered films. These errors in readings may result in a very

38

 

 

CR1
1 em = 0.05 Abs units

  
 

Sample a"IO
mm ‘8618 Wax 0 100°C
Reaction time : l0 min

 

 

0 r r
350 400

 

r 450 . 500 Y 550 . 600
Wavelength (nm)
Figure 10 Absorbance versus wavelength for catechol/IRM
#8618 wax solution reacted at 100°C for 10 minutes.

 

39

 

 

 

 

2.0
m
o
c
.8
L I.5 ‘
o
m
.0
< '1
El
0).) a E) [3
:3 1.0 ~ °
2 El
§ 1::
cu ‘0
C»
E
a) 0.5 .1
>
<1
0.0 r: . r . , .
0 100 200 300
Time (Min)

Figure 11 Average absorbance of the colored film product of
the catechol/IRM#8618 wax solution reacted at 100°C.

40
large spread of data points when individual runs are examined and
compared. Plots of the absorbance versus time for individual runs
were examined and indicated that data reduction by some method
should be attempted to condense the range of values determined by
the experiments. An example of this spread in data from individual
runs is shown in Figure 12, on the following page. This figure
includes interpolated curves which are shown by the lines in the
figure. The large spread in the data illustrate a reason for the data
reduction procedures and analysis.

The raw data used for this following analysis is included in
the appendix as Tables A-1 to A-3.

The data analysis method assumes that there are a constant
and set number of reaction sites in the film. This is assumed since
the catechol reacts with the titanium center incorporated in the
film. When the catechol reacts with the titanium site, this site is
assumed to become inactive with respect to further reaction. Using
the chemical reaction shown in equation 1, a kinetic rate expression

Catechol + Titanium Site --> Colored Complex (eq. 1)

can be constructed. Using the variables C for catechol, S for the
non-reacted site, and PS for the colored complex product it is
possible to derive the following expressions. Using the rate of
change of the available sites and assuming that this is first order
with respect to the number of open sites gives equation 2.

-_d§ = k"ICI'ISI
d1 (eq. 2)

The variable k in equation 2 is the rate constant. Assuming that the
concentration of the catechol is much greater than the number of
active sites, and therefore, approximately a constant will reduce
equation 2 to equation 3 where k’ is a pseudo-first order rate

41

 

 

 

 

 

 

 

I .5
_____-...—--.-—— l’
o) m ..........
2 /' a
t:
g 1.0-l r a
1.. .'
o I
to El.‘ __ I
a I _______ —"I
< 4 II "----".-
a’ I ..._—
2 If . O
“ I
o
'3; 0.5 7
or
0.0 . I r , .
0 100 200 300
Time (Min)

Figure 12 Absorbance of film product vs. time for three
catechol/paraffin wax solution runs at 65°C.

42
constant. Rearranging and integrating equation 3 using the limits

115 = k' ' [3]
dt (eq. 3)

of So to S as time goes from 0 to t results in equation 4. So is the
maximum and original number of open sites available in the film.
The variable 8 can be derived by a mole balance between the total

8 = 80 * exp(-k’t) (eq. 4)

number of sites and the number of sites that have reacted with the
catechol and have become inert. This relation given in equation 5
assumes the number of open sites(S) is equal to the number of

S = So - [P*S] (eq. 5)

total sites(So) minus the number of sites reacted and made
inert([P*S]). Substituting equation 5 into equation 4 to eliminate S
results in equation 6. This equation shows that the colored

[P‘s] = Sc *{1 - expl-k’tll ' (eq. 6)

complex ([P'S]) that is measured by the UV/Vis spectrophotometer
is exponentially related to time and proportionally related to the
maximum number of reaction sites in the film. This relationship
was used to least-squares fit the data determined by experiments.
To reduce the amount of data and to help eliminate errors discussed
above, the individual runs were averaged before being fit to equation
6. Averaged data for the various waxes and temperatures are given
in Table 7, on the following page.

The data in Table 7 was fitted to equation 6 using a least
squares routine from Kalida Graph with a Macintosh computer.

Table 7 Average relative absorbance of film product data reacted in

43

catechol/wax solutions at studied temperatures.

Paraffin Wax

 

 

 

 

 

 

 

 

 

 

 

 

Time 65°C 65°C 85°C 85°C 95°C
(Min) Saturated Unsat Saturated Unsat Saturated
0 0.000 0.000 0.000 0.000 0.000
5 0.597 0.661 0.588 0.391 0.855
10 0.600 0.702 0.635 0.526 1.200
15 0.633 0.765 0.680 0.502 1.280
30 0.639 0.790 0.732 0.579 1.345
45 0.677 NA NA NA ' 1.265
60 0.701 0.863 0.825 0.608 1.380
150 0.755 0.961 0.880 0.667 1.410
300 0.770 0.973 0.944 0.627 1.540
IRM Waxes
Time 90°C 100°C 110°C 120°C 130°C
(Min) #8618 #8618 #8618 #8618 Hewax
0 0.000 0.000 0.000 0.000 0.000
5 0.426 0.474 0.772 0.754 0.510
10 0.570 0.815 1.012 0.826 0.490
15 0.619 0.908 1.047 0.910 0.723
30 0.696 1.079 1.122 0.875 0.850
45 0.700 1.020 1.096 0.745 0.626
60 0.707 1.115 1.031 0.858 0.870
150 0.767 1.158 1.273 0.938 0.640
300 0.790 1.082 1.136 0.843 0.498

 

 

 

 

 

 

 

 

44
Figures 13, 14, 15, and 16, on following pages, depict the fit
of the data for experiments with saturated paraffin wax solution,
unsaturated paraffin wax solutions, IRM #8618 wax, and IRM Hewax,
respectively.

 

45

 

 

 

 

 

 

1.5
w A
8 o v
g o
L
O
B l
< E3
,_, III
E "’ iii are
E alt
g 0.5
g 316 6 (,C
E D 850
o) 0 95C
>
< 0 VIIfiri'l'ITIITII'UTIFTTW'II‘I
0 50 100 150 200 250 300
Time (Min)

Figure 13 Average relative absorbance and least squares data fit of
titanium film product reacted in catechol/saturated
paraffin wax for all temperatures studied.

46

 

 

 

   
  

 

1 3K
g 4 ¥
to . *
e 0.8“ x
8 -l
a ‘ Cl
4 '4 _________EJ
m 0.6: /['j—E]
>
'r'; 1‘93
E 0-4 3126570
3) 085°C
00.2
L.
0)
3i
0 T'TTTTUIITIFTII'I'[5115115'5

 

0 50 100 150 200 250 300
Time (l'lin)

Figure 14 Average relative absorbance and least squares data
fit of titanium film product reacted in catechol/unsaturated
paraffin wax for all temperatures studied.

 

47

 

   

 

1.5
Q)
U
5 o
P .D
L / 6_B—_—-:_——__—__—_—__.—-_—-._—.—-
8 I 0) D O —€5
.D I x
q X---x.---_---------—-----------------¥
3 at
:3
2
§ 0.5 ¥ 90°C
0’ :1 100°C
rig” 0110'}:
o) X 120C
>
4

 

 

IIITITTTTITTTTITIII‘TTTrlIITr

0 50 100 150 200 250 300
Time (Min)

Figure 15 Average relative absorbance and least squares data fit of
titanium film product reacted in catechol/IRM #8618
wax for all temperatures studied.

48

#

 

 

 

 

 

Q) -1
U .i
5 ~ ale 3"
.0 0.84
3 .
U) "*
D -i
4 06-1 * *
g) -1
I? a a"
2 0.4—
m at
0C .1
CD -1
U) ...
E 0.2‘
O
(D 4 +130C
> d
< 0*r1fitrfiTYl‘TtTTlTTfirfilTI'ITIU

O 50 100 150 200 250 300
Time (Min)

Figure 16 Average relative absorbance and least squares data fit of
titanium film product reacted in catechol/IRM Hewax
for all temperatures studied.

49
The values produced for k’ and for So from the graphs are
tabulated in Table 8.

Table 8 - So and k’ results of fit.

Wax Temp(°C) IsotAve Abs)! k'gMin-lz ICorrelationF
Paraffin Sat 65 0.689 0.347 0.973

 

Paraffin Sat 85 0.827 0.179 0.959
Paraffin Sat 95 1.380 0.191 0.961
Paraffin Unsat 65 0.874 0.219 0.979
Paraffin Unsat 85 0.611 0.182 0.990
IRM #8618 90 0.729 0.154 0.994
IRM #8618 100 1.098 0.122 0.951
IRM #8618 110 1.126 0.225 0.836
IRM #8618 120 0.858 0.415 0.839
IRM Hewax 130 0.694 0.210 0.961

 

 

 

 

 

 

 

 

Examination of the data does note lead to any conclusions
based on numerical trends. Also, 50 can not be related directly to
any physical constant since the absorbance is an indirect
measurement of the colored complex concentration. So is related to
the total number of sites available for reaction and should be
relatively constant throughout all the temperatures and waxes. This
consistency results from the film being of a constant thickness,
consistent preparation, and constant beam area in the UV/Vis
spectrophotometer. With this constant volume being measured and
consistent film stoichometry, the number of available sites should
remain as a constant.

Using these results for the k' values allows the calculation of
the activation energy using the Arrehenius equation which is
linearized in equation 7. A plot of the In(k’) versus 1/T results in

Fl ‘ T (eq. 7)

Figure 17 for the IRM #8618 data points. This graph has two best fit
lines added to show the agreement of theory to data. One line uses
all four data points for this wax while the other line does not use
the 90°C data point for IRM #8618 wax. As the graph illustrates, the
fit is much better without this data point. This may be caused by
the reaction taking place near to the melting point of the IRM #8618
wax(MP=80 to 84°C). This may have resulted in problems due to the
time taken for the excess wax on the slide to liquefy when the slide
was reinserted into the liquid wax solution. This lag between the
start of the reaction and the insertion of the slide into the wax
solution, in effect, would increase the effective rate constant. This
arises if the rate constant is expressed as the reaction rate divided
by the reactant concentration. With the delay in melting occurring,
the visible concentration of reactants is effectively reduced causing
the rate constant to increase. This increased rate constant when
converted to the Arrhenius equation by the natural log would tend to
decrease the In(k') value as seen in Figure 17, on the following page.

Using the slope and intercept values given in Figure 17 for the
calculation of the activation energy(Ea) gives values of 1.08 KJ/mol
for the data incorporating all points and 0.607 KJ/mol for the data
that excludes the 90°C point.

Figure 18, on the second page following, is a Arrhenius plot of
the paraffin wax saturated and unsaturated samples. This plot also
shows that the low temperature samples(65°C) appear to have a
increased k' value and decreased In(k’) value possibly caused by the
reaction occurring near the melting point of the wax as discussed
above. Since only three points were found for the saturated paraffin

51

 

 

 

 

-0.s ,
1 without 90 C point
i / g -21.942-6971.1x R‘2=1.000
-1.0 -
with 90°C point
I g = 11.783 - 5049.4x R2 = 0.731
.x '1
\E -1 S j i
4
'1 O
-2.0 ~
.1
l
‘25 v i ' l '
0.0025 0.0026 0.0027 0.0026

l/Temperature(K)

Figure 17 In(k’) versus 1/T from titanium film reacted with
catechol/IRM #8618 wax solution.

52

 

 

 

 

-1.0
o In(k' Saturated) '3
o In(k' Unsaturated)
-1.2 '-
3‘; -1.4 4
J
O
-1.6 -
E
8
“1.8 v j r T 7
0.0027 0.0028 0.0029 0.0030
l/Temperature(K)

Figure 18 In(k’) versus 1/T from absorbance of titanium
film reacted with catechol/paraffin wax data fitting.

53
wax reactions, no observations on trends can be observed. Also, for
the unsaturated paraffin wax solutions, only two points are plotted
and again no generalizations can be made.

To summarize, this analysis is based on a number of available
sites for reaction in the film. This theory allows the calculation of
a constant maximum number of sites for the films. Analysis of the
data using the kinetic model results in values for this maximum
number of sites that do remain relatively constant over all
conditions. This model also allows calculation of a pseudo-first
order rate constant and subsequent calculation of the activation
energy. Paraffin wax samples do not give very good agreement of
activation energy between expected and experimental and a possible
explanation of this is discussed above. The IRM #8618 wax does
give reasonably good results for the rate constant and activation
energy. IRM Hewax was not analyzed since only one data point wax
taken.

5. CONCLUSIONS

The purpose of this study was to determine the feasibility of
using a film-based sensor for time-temperature history profiles. A
titanium-based film was used as a colorimetric recorder 0f the
time-temperature history of the ambient environment. This film
would react with indicator chemicals dissolved in a frozen solvent.
As the solvent reaches its melting point, reaction between the
indicator and film would begin causing a color change of the film.
Studies were performed on both low (-20 to 30°C) and high (65 to
140°C) temperature sensors.

Optimization of the film construction and indicator chemicals
was performed for both temperature ranges. Catechol was the
indicator chemical of choice for both temperatures. A valeric/lauric
acid based titanium solution appears to be the most effective at
producing a film for both temperature regimes. Solvents for the low
temperature region that were used include dimethyl succinate and
diethyl fumarate, while different wax blends were utilized for the
high temperature region.

Studies were made on the feasibility of the low temperature
sensor with indications that the colorimetric reaction would not
quench upon return to temperatures below the freezing point of the
solvent. This low temperature sensor may be useful as an indicator
that the ambient environment has achieved a temperature above the
freezing point of the solvent. This deficiency of the sensor caused a
shift in emphasis to the high temperature sensor. The food
industries need for a high temperature sensor and the already
available low temperature sensors supported this shift.

High temperature sensors were studied using various wax
blends from temperature of 65°C up to 140°C. Temperatures above

120°C caused rapid saturation of the spectrophotometer readings.

54

55

Analysis of this data was performed using a saturation type rate
analysis using the number of titanium reaction sites as the limiting
reactant. This model allowed line fitting of the experimental data
with good results for the catechol/IRM #8618 wax solutions reacted
to the titanium film. Absorbance values of the colored film were
least square fitted using this model and allowed calculation of the
effective rate constant and also a value proportional to the total
number of available titanium centers in the film.

Quenching studies of the high temperature sensor indicate that
the reaction does not proceed appreciably below the freezing point
of the wax solvent. Use of the calculated data produced by the
saturation model analysis could allow the integration of the
recorded values from multiple melting point solvent sensor strips.
This integration of the sensor readings would be used to determine
the time—temperature history of the environment. Although, initial
data curves are available in this paper, refined data should be
obtained from any manufactured sensors produced in the future to
take into account the manufacturing process and completed
construction. Also formulas need to be developed to relate a
possible changing thermal profile to the absorbance readings of the
sensors.

In summary, the low temperature (-20 to 30°C) sensor studied
will provide maximum ambient temperature information with the
use of the appropriate solvents. The high temperature (65 to 140°C)
sensor appears to be effective at determining the time-temperature
profile of the steady-state surroundings and further research is
needed to analyze the sensor readings to changing thermal
conditions.

6. RECOMMENDATIONS FOR FUTURE WORK

Use of a cold temperature sensor appears feasible for
determination of the maximum temperature of the environment.
More study on this device should be performed if an application for
this type of sensor is determined. Methods of construction that
would permit the sensor to remain in the inactivated state must be
determined. Different concentrations of the indicator and the use of
different indicators should also be studied to allow more precise
measurements. Different concentrations and indicators may allow
this sensor to be converted to a true time-temperature device.

The high temperature sensor requires a more complete study
on the kinetics of the indicator at different temperatures.
Additional indicators and solvents should be determined to extend
and define this high temperature range. If manufactured sensors are
produced, these sensors should be tested to determine and refine the
calibration curves as discussed in section 4. Experiments should be
performed to confirm or disprove an accurate time-temperature
measurement compared to the changes in the actual thermal
environment. Mathematical models are available to determine the
time spent by the indicator in various temperature ranges as a
function of the reaction extent and reaction start temperature.
These models should be compared to this sensor to confirm a method
of determining the time-temperature profile over changing
temperatures for various times.

Table A-1

7. APPENDIX: RAW DATA

Raw data of the absorbance of titanium film colored

product reacted in catechol/paraffin wax solution.

Paraffin Wax @ 65°C Saturated

 

 

 

Absorbance
Time(Min) #1 # 2 # 3

0 0.000 0.000 0.000

5 0.540 0.615 0.645
10 0.480 0.660 0.660
15 0.591 0.615 0.705
30 0.552 0.660 0.705
45 0.615 0.645 0.771
60 0.690 0.675 0.740
150 0.735 0.750 0.780
300 0.630 0.810 0.870

 

 

 

 

 

Paraffin Wax

@ 65°C Unsaturated

 

 

 

 

 

 

 

 

 

 

 

 

 

Absorbance

Time(Min) #1 11 2 #3 #4 #5 11 6
0 0.000 0.000 0.000 0.000 0.000 0.000
5 0.611 1.700 0.802 0.665 0.513 0.512
10 0.655 1.995 0.785 1.039 0.458 0.571
15 0.664 2.962 0.835 1.193 0.516 0.616
30 0.698 NA 0.963 0.994 0.589 0.708
60 0.854 NA 0.979 1.131 0.607 0.742
150 0.922 NA 1.197 1.253 0.621 0.811
300 0.939 NA 1.062 1.330 0.678 0.858

Paraffin Wax @ 85°C Saturated
Absorbance

Time(Min) #1 # 2 # 3 # 4 # 5 11 6
0 0.000 0.000 0.000 0.000 0.000 0.000
5 0.645 0.439 0.615 0.782 0.617 0.427
10 0.643 0.470 0.613 0.854 0.721 0.510
15 0.736 0.438 0.569 1.013 0.729 0.592
30 0.789 0.561 0.736 0.981 0.737 0.587
60 0.788 0.694 0.913 1.028 0.840 0.689
150 0.987 0.657 1.079 0.872 0.955 0.731
300 0.957 0.681 1.188 0.881 1.129 0.829

 

 

 

 

 

 

 

57

 

 

58

 

 

 

Table A-1 (cont’d)
Paraffin Wax @ 85°C Unsaturated
Absorbance

Time(Min) #1 #2 #3 #4 #5 #6
0 0.000 0.000 0.000 0.000 0.000 0.000
5 0.555 0.443 0.379 0.364 0.467 0.141
10 0.617 0.510 0 660 0 440 0.705 0.223
15 0.657 0.527 0.497 0.479 0.562 0.293
30 0.693 0.565 0.798 0.532 0.481 0.405
60 0.738 0.603 0.560 0.635 0.608 0.501
150 0.754 0.614 1.000 0.567 0.541 0.527
360 0.803 0.685 0.585 0.577 0.553 0.556

 

 

 

 

 

 

 

Paraffin Wax @ 95°C Saturated

 

 

 

Absorbance
Time(Min) #1 # 2 # 3
0 0 000 0.000 0.000
5 1.080 0.150 1.335
10 0.990 1.350 1.260
15 1.230 1.185 1.425
30 1.230 1.455 1 350
45 1.050 1.545 1.200
60 1.110 1.360 1.650
150 1.170 1.740 1.320
300 1 230 1.590 1.800

 

 

 

 

 

 

Table A-2

Raw data of the absorbance of titanium film colored

59

product reacted in catechol/IRM #8618 wax solution.

IRM #8616 wax @ 90°C

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Absorbance
Time(Min) #1 #2 #3 #4 #5 #6
0 0.000 0.000 0.000 0.000 0.000 0.000
5 0.660 0.750 1.080 0.450 0.450 0.420
10 0.660 0.750 1.170 0.600 0.660 0.390
15 1.260 0.530 1.260 0.600 ‘0.600 0.540
30 0.700 0.960 1.110 0.570 0.630 0.600
45 0.900 0.660 1.320 NA NA NA
60 1.290 0.720 0.810 0.570 0.690 0.660
150 1.170 0.690 1.470 0.660 0.610 0.660
300 0.930 0.660 1.500 0.690 0.840 0.750
IRM #8618 Wax @ 90°C (cont'd)
Absorbance
Time(Min) #7 #8 #9 #10 #11 #12
0 0.000 0.000 0.000 0.000 0.000 0.000
5 0.000 0.000 0.000 0.255 0.450 0.600
10 0.240 0.420 0.150 0.690 0.600 0.510
15 0.300 0.330 0.150 0.750 0.690 0.420
30 0.330 0.480 0.540 0.840 0.630 0.960
45 NA NA NA 0.330 0.750 1.260
60 0.570 0.600 0.570 0.720 0.840 0.450
150 0.720 0.420 0.870 0.780 0.960 0.000
300 0.720 0.450 0.870 0.750 0.900 0.420
IRM #8616 wax @ 100°C
Absorbance
Time(Min) #1 #2 #3 #4 #5 #6
0 0.000 0.000 0.000 0.000 0.000 0.000
5 1.590 1.080 1.170 0.900 0.390 1.080
10 1.470 1.200 0.930 0.390 0.330 1.260
15 1.680 1.200 1.470 0.630 0.600 1.320
30 2.318 1.260 1.140 0.360 0.360 2.052
45 1.620 1.530 1.170 1.470 0.600 1.750
60 1.590 1.500 1.230 0.330 0.450 . 2.336
150 1.710 1.500 1.200 1.170 0.570 1.710
300 1.770 1.590 1.320 0.270 0.510 1.943

 

 

 

 

 

 

 

 

 

 

6)

Table A-2 (cont’d)

IRM #8618 Wax @ 10000 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Absorbance
Time(Min) #7 #8 #9 #10 #11 #12
0 0.000 0.000 0.000 0.000 0.000 0.000
5 0.150 0.270 0.660 0.480 0.150 0.960
10 0.330 0.540 0.670 0.720 0.720 1.020
15 0.420 0.810 0.780 0.870 0.150 0.960
30 0.540 1.200 1.080 1.050 0.930 0.660
45 0.510 1.126 0.510 1.080 0.660 0.210
60 1.170 1.060 1.110 1.050 0.930 0.600
150 1.294 1.320 0.600 1.110 0.840 0.870
300 0.960 1.170 0.750 1.140 0.960 0.600
IRM #8616 wax @ 110°C
Absorbance
Time(Min) #1 # 2 #3 #4 #5 #6
0 0.000 0.000 0.000 0.000 0.000 0.000
5 0.900 1.320 1.350 0.840 0.765 1.200
10 0.960 1.170 1.650 1.080 1.020 1.530
15 1.020 1.080 1.470 1.080 NA 1.650
30 1.155 1.215 1.710 1 230 NA 1.723
45 1.380 1.170 1.590 0.810 NA 1.830
60 1.200 0.780 1.830 1.080 NA 1.710
150 1.830 0.870 1.710 1.050 NA 4.850
300 1.800 0.570 1.862 1.100 NA 2.154
IRM #8618 Wax @ 110°C (cont'd)
Absorbance
Time(Min) #7 #8 #9 #10 #11 #12
0 0.000 0.000 0.000 0.000 0.000 0.000
5 0.570 0.090 0.750 0.630 0.120 0.720
10 0.930 0.780 1.020 0.720 0.390 0.900
15 0.810 0.990 0.750 0.900 0.810 0.960
30 1.110 0.870 1.350 0.930 0.120 0.930
45 0.540 1.260 1.440 0.930 0.120 0.990
60 (1.990 1.080 0.930 0.690 0.090 0.960
150 0.480 0.810 0.600 0.570 0.210 1.020
300 0.570 0.840 0.960 1.230 0.210 1.200

 

 

 

 

 

 

 

 

 

 

61

Table A-2 (cont’d)

IRM #8616 wax @ 120°C

 

 

 

 

 

 

 

 

 

 

 

 

 

Absorbance

Time(Min) #1 #2 #3 #4 #5 #6
0 0.000 0.000 0.000 0.000 0.000 0.000
5 0.765 1.200 0.840 1.050 1.050 1.110
10 0.750 1.050 0.795 1.230 1.230 1.260
15 0.720 1.080 1.080 1.380 1.230 1.320
30 0.600 1.410 0.750 1.470 1.290 1.680
45 0.870 1.410 0.720 1.170 1.560 1.560
60 0.600 1.470 0.660 1.500 1.350 1.440
150 0.630 1.590 0.690 1.440 1.620 2.100
300 0.870 1.725 1.170 1.350 1.410 1.950

IRM #8618 Wax @ 120°C (cont’d)
Absorbance

Time(Min) #7 #8 #9 #10 #11 #12
0 0.000 0.000 0.000 0.000 0.000 0.000
5 0.870 0.210 0.900 0.570 0.270 1.260
10 1.140 0.360 0.900 0.960 0.460 0.990
15 1.170 0.180 0.660 1.380 0.600 1.350
30 1.260 0.150 0.930 0.840 0.450 0.960
45 1.350 0.330 0.540 0.180 0.270 0.540
60 1.290 0.390 0.540 0.300 1.110 0.990
150 1.170 0.000 0.570 0.930 1.200 0.930
300 1.193 0.090 0.540 0.120 0.270 0.840

 

 

 

 

 

 

 

 

 

62

Table A-3 Raw data of the absorbance of titanium film colored
product reacted in catechol/IRM Hewax wax solution.

IRM Hewax @ 130°C

 

 

 

Absorbance * ,
Time(Min) #1 # 2 # 3
0 0.000 0.000 0.000
5 0.420 0.300 0.810
10 0.060 0.300 1 110
15 0.360 0.600 1.209
30 0.930 0.570 1.050
45 0.240 0.480 1.157
60 1.243 0.210 1.157
150 0.510 0.240 1.170
300 0.210 0.210 1.073

 

 

 

 

 

8. LIST OF REFERENCES

1. Taoukis, Peter S., Bin Fu, Labuza, Theodore P. Time-Temperature
LndjcatomFood Technology, October(1991), pg. 70-82.

2. Blixt, K.G., Tornmarck, S.|.A., Juhlin, R. Salenstedt, K.R., and Tiru,

M. 1977. Eozymatic substrate comoosition adsorbed on a carrier. US.
patent 4,043,871.

3. Agerhem. M.. Nilsson. L. 1981. WWW
thereot, US. patent 4,284,719.

4. Shafer, J.A. 1989. m ii 11 f r nr ll
alcono|s_oL_aan_es. US. patent 4,795,714.

5- Ja'i'lSki. T-J-. 1991. WWW
0.0m. US. patent 5,085,802.

6. Manske, W.J., 1973. Selected time interval indicating device, US.
patent 3,954,011.

7. Patel, G.N., Freeland, A.F, Boughman, RH, 1976. Lime-_temoeLatuLe
history indicators. US. patent 3,999,946.

8. Patel, G.N., 1980. Vaoor-ohase moving boundary indicator. US.
patent 4,195,057.

9. Patel. G.N., 1980. WWW
US. patent 4,195,058.

10. Allmendinger, T., 1984. Process for monitoring the history of

‘IIO‘ ._ l‘ of o-‘o- 0 -| o 00_ no so 0

. US. patent

 

4,432,656.

11. Arens. RR. 1984. W
indicator. US. patent 4,428,321.

63

64
12. Kang, .K..S, Muna, 8., Robinson, J., Maher, E.F., 1989. l_ndjcato_[

U. S. patent 4, 804, 275.

13. Karr, L.J., 1981. Time-temperature indication, US. patent
4,277,974.

14 Anderson,M., Gieselmann, M., Qunyin Xu, [items and Alumina
W265. Journal of Membrane Science, 39(1988), pg.
243-258.

15 Dunuwila, D., Gagliardi, C. Berglund, K. W
Eilms Produced by Sol-Gel Er rocessing, Internal Report, 1989.

16 Kirk-Othmer, Encyclooedia of Chemical Technology, 3rd Ed. Vol
23. John Wiley 8 Sons, New York, 1983. pg. 176-245.

17 Yoldas B...E 810W

Hyidrolytc Polycon nnde nsation Parameter rs. Journal of Materials
Science, 21(1986), pg. 1087-1.092

18 Masterton, W., Slowinski, E., Conrad, L. Wis, 6th
Ed., Saunders College Publishing, Chicago, 1985. pg 634-663.

19 Cotton, A. F., Wilkinson, G. Advanced Inorganic Chemistry, 5th Ed.
John Wiley & Sons, New York, 1988. pg 474-475.

20 Pierpont, Cortlandt G., Buchanan, Robert M. LansjtjoLMetal

mlx f-an inn -mi inn r1 hl
Ligand; Coordination Chemistry Reviews, 38 (1981). pg 45-87.

21 Aldrich Chemical Company. WWW

1_9_9_2-_1_9_9_3_. Aldrich Chemical Company, Milwaukee. 1992.
22 Sigma Chemical Company. Biochemical s, or rganic Qom mnooo nds, for

WW2 Sigma Chemical Company,
St. Louis, 1992.

23hMrklnexAnEnl ifhmilDr n
Blologjcats.11th Ed. Merck & Co., Inc. Rahway, NJ 1989.

65
24 Torgerson, B.A., Dunuwila, D., Berglund, K.A., Raman and Sorface

II!‘ ‘0 I15... 0‘ o H o -.|.l -._H. ,MFiS

Symposium Series 271, 1992, Pg 65-70.

25 Barrow, Gordon M. Ehysical Chemistry, 5th ed., McGraw-Hill Book
Company, New York, 1988. pg. 576-577.

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