THE PROTON RESONANCE ABSORPTION IN LIQUID CRYSTALS Thesis for Degree of Master of Science MICHIGAN STATE COLLEGE HERBERT A. MOSES 1953 WI"INN“lllllllllUUlHl!IIHJIHIIIIIIIHIHUIHIHIH 301774 9767 LIBRARY Michigan State University This is to certify that the thesis entitled WA. :- 40¢ 25 0-: 64¢ c4. Z477 £0» av.” 61/ «.x'a/ 61/4 71-1,;- presented by A 44/ ’4 777,7“ has been accepted towards fulfillment of the tetIuirements for & degree in @115: Mfi professor Date 7%m; mm 0-169 ,. -——,—-— afiwi I PLACE IN REI'URN Box to remove this chedcout from your record. To AVOID FINES return on or before date due. MAY BE RECALLED with earlier due date if requested. DATE DUE DATE DUE DATE DUE 1m cICIRCJDdoOmpOS-p.“ THE PROTON RESONANCE.ABSORPTION IN LIQUID CRYSTALS By HERBERT A. MOSES A THESIS ' Submitted to the Schoolof Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Physics 1953 Acknowledgement I wish to express my utmost gratitude to Professor Robert D; Spence for his patience and sound guidance in the. respective phases of this problem, and for his undying enthusiasm which has been a constant source of inspiration. [AerJ' AL 54035 ‘7’ ‘l f‘K‘)‘l CONTENTS INTRoDUCTION.................................................1 ExPERINENTAL APPARATUS.......................................2 LINEWIDTH CHARACTERISTICS.OE SODIUM STEARATE.................3 LINENIDTH CHARACTERISTICS or SODIUM:CLEATE...................4 GRAPHS 0F LINEWIDTH vs. TEMPERATURE FOR SODIUM STEARATE AND SODIUM WEATECC...O.OOCOOOOOCOO.OOCCCCOOOOOOOOCOOOO00......5 LINENIDTH CHARACTERISTICS OF CHOLESTERXL BENZOATE............6 THE PROTON ABSORPTION LINES or SODIUM STEARATE AND SODIUM m‘EATEQOOOOOOOOOOOOOOOOCO.CO...OOOOOOOOOOOQOOOOOO.OO'OOOO..'C7 THE PROTON.AssoRPTION LINES or SODIUM OLEATE AND CHOLESTERIL BENZOATEOOOOOQOOOooooooo000.000.000.000.00.00000000000000008 LINEVIDTH CHARACTERISTICS OF ANISALDAzINE....................9 GRAPH.OE LINEwIDTH vs. TEMPERATURE FOR ANISALDAZINE.........10 PHOTOGRAPHS OF THE PROTON ABSORPTION LINE OF ANISALDAZINE...11 THE ROTATION ExPERIMENT.....................................12 THEORY......................................................13 APPENDIX (30 CYCLE CENERATOR)...............................18 WAVE SHAPES PERTAININC To THE 30 CYCLE CENERATOR............19 SGHEMATIC DIAGRAM OF THE 30 CICLE CENERATOR.................21 c I A I I 0 o I . Q ‘ . I § 9 4 o 1 ~ 0 ~ 0 O O O O 9 V I O O I O I l C O I I D O I I o . 4 a .‘L o O Q...- 0 o I O O O . . o 0 V V - n . . vt__ __S —.— _\m- -4 INTRODUCTION Recently it has been shown that the proton resonance of the liquid crystal, parazoxyanisole, exhibits an anamalous structure.1 This thesis reports additional work on liquid crystals suggested by the initial discovery. Prior to the work presented here, study has been made solely on the ne- matic, thread-like liquid crystals and it is the purpose of this thesis to report the absorption line characteristics of other types of Insomorphic (liquid crystalline) substances. It is believed that the liquid crystalline state con- sists of an ordered arrangement of groups. (The word ’crys- talline” has been assigned to indicate the property of anis- otropy, characteristic of this phase.) Three types of liquid crystals exist: nematic, smectic, and cholesteric. The nematic liquid crystals possess long molecules which main- tain come definite orientation in.the intermediate state. In the smectic and cholesteric compounds we have a slightly different situation. The molecules of these substances are in the shape.of planes which lend.to the overall nature of a planal meeonorphic state. The main difference between a smectic.and cholesteric structure is that the former consists of planes Whose thidkness is the order of one molecule, while 1. R.D. Spence, H.A. Moses, P.L~ Jain, “The Proton Magnetic Resonance in Liquid Crystals,“ Jogggal of Ghemigal Eggsigs, February, 1953, P. 2080 the latter consists of planes from 500 to 5000 molecules in thickness.? ‘EXPERIHENTAL APPARATUS The apparatus used consists of an electro-magnet3 oper- ated at 7300 gauss, a “twin-T" radiofrequency bridge, oscill- ator, preamplifier, reseiver, and cathode-ray-cscilloscope- This apparatus is essentially the same as that discussed by Villaire‘ in his thesis. The only new component added to the abOve is a thirty cycle generator which is described in detail in the.appendix. The linewidth variations were measured by means of a timing sigal and using the relationship AH' It‘UHM in which H“: the maximum value of the modulating field, and Jr 3 the time duration corresponding to the linewidth, It is believed that the measurements taken contain.nc more than '5 10 7, experimental uncertainty, the limitations on linewidth measurement being 0.1 gaussa 2. Glasstone, ngtbgok g; ghysigal ghemistry, pgs. 504 to 508. 3. Luck, Jerome Arthur, igngand‘anstrugtion 9f a Labor- atogx Elegtggmagget, esis, Michigan State College,.l950. 4.. Villaire, Alfred Edmond, The Radiofreguencz Bridge Methgg 9f Detegting Nuclear Resonange Si als, Thesis, Michigan State College, 1952.. A -2- RESULTS SOEEUM STEARATE [CH3 “(CH3)“:- 8 -' 0 r‘ ”4] Sodium Stearate has been used as a typical smectic liquid crystal and the resonance absorption line observed. Above 260°C. this sample of sodium atearate is in the liquid state. The linewidth measurements indicate a width of approximately 1.10 genes with a slight broadening at the lower limit of the state to 1.15 gauss. When the transition point to the liquid crystal state is reached (26000.), the linewidth increases to 1133 gauss and remains constant until 20000.. As the substance cools below this solid transition point, a marked increase in linewidth occurs. The average width of the line in the solid state is 2.8 gauss. The most important observation made is the fact that a single line exists in all states with only the loss of wiggles (gping from liquid-to liquid crystal state) and broadening, giving indication of a change taking place in the substance.5 5. No eVidence of an unidimensional melt taking place at 70°C. has been observed in the form of a linewidth change. -3- SODIUM CLEATE o EH3-(CH,)7—cu =c H-(c».)7-£-o«A/A.J Sodium oleate behaves much the same as sodium stearate. Sodium oleate is also a smectic type liquid crystal with an upper transition point of 235°C. (liquid to liquid crystal phase) and a lower transition point of 135°C. (liquid crystal to solid state). Throughout the liquid state a steady line- width of 0.69 genes is maintained and finally broadens to 1.17 sense at the transition point 235°C. . (The linewidth change is more distinct than that of the stearate.) At 135°C. another sharp transition occurs as the liquid crystal sblidi- fies. In the solid state thelinewidth becomes 1.37 gauss. Here again, as in sodium stearate, one line exists in all these states. It is believed that a disruption of the polar bonds occur in these smectic substances On heating from the solid state, to give rise to this liquid crystal stats.5 (See graphs of AH vs. temperature) 6. Galley, Willard a Puddington, "Physical States of Anhydrous Sodium Salts," Canadian Jggrnal of Research, 1943, p. 202. AH gmss ‘i—r—t—L. fl] ii ”0 no TEIIP.‘c SODIUM STEARATE L' LIQUID STAT! L00 Ll 0WD cIYS‘l’IL STAT! c-ccuc UTA?! 1 A a“. 1". 2‘0 TEMP. Cc no no SODIUM OLEATE 5’. cu, H CH -—-cu‘—cu‘—CII.— c —c H: /" C": m. v, -. a e ‘ . 1. w . '3 ,.- .s. "1H . a! he cfoio~,~r c eiryrintl, o‘ciowtvryi {YWLHann, i,:o ..n t‘c “Hectic ccm'ouniw leachifiol Ibovo, alao exhihits rho r0- "Cpincv lino thr u hcut t”? licuid, licuil crvdtil, an! 10111 nfilifl“. In thfi lifui! “5'2? the line is O.”€ hive“. .fi we tprro's‘ ‘** trircttion point to the li'ufii crrntwl attic ("”‘ FC‘I, , f‘t} li'vewv‘n'n‘w fr~ .97 'rxuw‘z in! 11 an "ulicklg' - Smlm STEMATE WU“ STEMATE LIQUID STATE TMNTDN FONT FROM LIQ. HODULATING FIELD -'-‘- 3| v. TO LIOJJYBTAL 51'“ 1m: ale mu. 4 coo/us. In I scum "mu. soouu "can: ucuio mum. sun: SOLID STAT! NODULATIIG FIEw:30'. MODULA‘IINB FILD=64vo Tm: SIGNAL Q0050!» Tm: SIGNAL «co/m. SONIA O LEATE LI OUIO STAT E L "NUUTING FIELD’3OW SODIUM OLEATE TIME SICNAL 4.00/606. LIQUID CRYSTAL STAT! SODIUM OLEATE CHOLESTERYL BENZOATE SOLID STATE LIQUID STATE MODULATING FIE L.D= 45v MODULATINO FIELD 7- 30v TIME SIGNAL 4809's“. TIRE SBNAL 4800/3“. CNOLESTENYL ENZMTE CHOLESTERYL BENZOATE TRANSITION POINT FROM LIQUID CRYSTAL STATE LIQ- TO LIGCNYSTAL STATE MODULATINO FIELD 330'. TIME SIGNAL QOOO/uc. newsman. Benzene souo STATE uoouumuc FlELD=30v mac SIGNAL 4900’s"- assumes the value of 0.95 gauss as the substance passes inte the liquid crystalline state. This value remains quite con- stant throughout the mesomorphic state until the lower transi- tion point (139.1°C.) is reached. In the solid state the average linewidth is 1.29 gauss. ANISALDAZINE 2:.- ’5—5' // \ C I-IJO— < g}..?=N-MBC-C\ >C"OCHJ I \\c.—cfl%y H 14 IC:=:C u N I! The most exciting compound of those investigated is anisaldazine, a nematic type liquid crystal. In the liquid state the linewidth is 0.72 gauss from 207°C. to 177°C. . At this point the line begins to widen until we reach 0.95 gauss, an increment above the transition point to the liquid crystal state (180.7OC.). As the substance goes into the mesomorphic state, the line splits into three lines, the center of which is the greatest amplitude. The peak to peak distance of the outer satellites was noted carefully as the substance cooled to the solid state, and a variation of this distance plotted against temperature. This variation is not linear, but very nearly so. The total -g- LC I?! “:0 I" 0;. TE “ p, F c LIO. LI0.0NY.TAL I ‘OLIO STATE. OF CHOLESTERYL BENZOATE $94? . Lat—J m no no nun’c snuuu Pun vamnnou IN THE ucmo taunt. "an or ANISALDAZINE IO- A NISALDAZINE LINES LIQUID STATE assumes or LIQUID CRYSTAL STATE uccuunuc nn0=zev ucouurme FIELD=25v Tm: SIGNAL lance/at. mas sucmu. IOpOQ/eec. INLE OF LIQ. CRYSTAL STATE END OF LIQ-CRYSTAL STATE IODILATING FIELD=ZOv NODULATING FIELD’ISJI TIIE SIGNAL IOOOO/eec. TINE SIGNAL 9625/3“. SOLID STA TE HODULATIIIG FIELO=84.5 v. TIME SIGNAL /965 sec. ’1. range comprises 1.36 gaues, the maximum value being 3.76 genes at 180.7°0; and the minimum value being 2.40 gauss at 162.1°c. . The line observed from the solid state or anisaldazine is slightly greater than 3.8 genes. A measurement was made of the relative amplitudes of the main and satellite peaks, the average of forty readings giving a ratio of center peak amplitude 2.14 satellite peak amplitude l A This is in good agreement with theoretical predictions (see thOOrY) e7 ROTATION EXPERIMENT Under the assumption that the three component line of the liquid crystal state may be annihilated or its shape transformed by breaking the group structure, the sample was rotated, and a "cork-screw" object was rotated in the sample of anisaldazine. For thisturpose a small air turbine motor 7. sThis portion or the thesis has been presented at the Rochester New York meeting of the American Physical Society, sunejfa, 1953. -1—2- was used with a variable speed control. A negative result was obtained in all cases, the three line structure persist- ing throughout rotation. THEORY It is believed that the broadening of the absorption line, such as that observed in the smectic and cholesteric liquid crystals upon a decrease in temperature, is due to a hindered rotation of the molecules. Representing this schematically we might picture it as follows: Qom rims HIWDERED / BOTATIaNs STRouc-r LAVEMHINV+ —‘ WTEMP. For the case of anisaldazine we have a different situa- tion. The three lines arise from the basic configuration of the molecule and its rotation about an axis parallel to the 8. H. S. Gutowsky, G.E. Pake, “Structural Investigations by Means of Nuclear Magnetism, Hindered Rotation in Solids," Jogrnal of Gaggiggl Physics, vol. 18, February, 1950. P56. 1 2-170e -1-3’... applied magnetic field.. In order to understand this phenomenon it is necessary to redraw the anisaldazine molecule, taking into.account the angle the an bond makes with the center structure. \c— c/c-_\C—C-N=—N—c—//C“C\C {TX \c—c/ " H \=C'/ \ H in not us analyze the molecule from the end group to the NJof fieN. It can be seen from the diagram that the vector distance between the end group protons will be continually changing.as the molecule rotates about the x.axis, since the angles of these hydrogen.atoms change.. Due to this variation, an aver- aging out process takes place and one single line results from all three (when applied to the whole molecule, six) pro- tons. I The same type of reasoningidoes not apply to the H's in the benzene ring. Here the proton distances are fixed and the symetry of rotation leads us to a consideration of each proton individually. The interaction of protons on opposite sides.of the benzene ring may be neglected, since the distances between -14.- these are too large.9 However, the two adjacent protons.on each side of the ring act as a dipole and give rise to the two satellite peaks. Each set of two protons contribute to one-half of the amplitude of these peaks. Since there are; three protons in the end group, plus one proton in the center group (for half the molecule) which give rise to the single line, and effectively two protons in the benzine ring giving rise to the satellite peaks, the ratio of amplitudes should be 4:2 or 2:1. This number is verified quite well by the data cited above.10 A quantum mechanical argument applied to the above two H's in the benzene ring leads to an elementary explanation of why we might expect two lines to arise from a dipole in an applied magnetic field. The dipole may be orientated in three different ways with respect to the applied field, both parallel, both anti- parellel, or one parallel and the other anti-parallel to the field. This is shown in the drawing below. 9. The field due to a dipole of magnetic moment’A) , at a distance rr from the dipole = a2;: . 10. The area measured under the major and satellite peaks will bear the same ratio. The above measurement is made on the assumption that the three linewidths are equal. This is very nearly so. -15- HIGHEST E/szay STATE; Lewes-r E/vuzty STATE Zeeman Energy States In "A" above, the protons are such as to require a max- imum amount of energy to maintain this orientation and thus belong to the state of highest energy. The minimum state is that of ”C” since here the protons are aligned with the applied field. On the center diagram above, "B", we have a neutral orientation giving rise to the 0 energy state. Considering the dipole alone and the individual fields of each proton, we get an additive effect in case "A". The field of proton ”1" tends to superimpose on that of ”2" and likewise, .16.. the field of proton ”2" tends to reinforce that of "l". The total effect is one of an even larger energy required to main- tain the fixed orientation. This raises the energy level to T1 in the diagram. We can use a similar argument to explain the lowering of the energy level to T4 in case "C", however, now considering a partial annulment of fields. -We must apply a quantum argument for the splitting of the 0 state into two separate energy levels, but this will not be described here. Whereas equal transition existed between the three initial energy states, now only unequal transitions may occur between the triplet energy states (labeled T in the diagram). This gives rise to two transition frequencies possible for the hydrogen atoms. Thus the absorption line splits.11 ll. R.D. Spence, Colloquium, Michigan State College, April 8, 1953. and H.S. Gutowsky, a private letter to R.D. Spence upon publication of the article on para- zoxyanisole. -17- , APPENDIX The only new component added to the circuit described by V’illaire12 is a thirty cycle generator. A diagram and de- tailed explanation of various stages of this circuit is shown on the following pages. Essentially, a sixty cycle, 115 volt signal is impressed on a 6SN7 phase inverter and choke in the first stage. Due to the inductance, “(l/2t drops to 0 and gives rise to the wave shape shown in figure C. This resultant wave form is sent through the multivibrator and a thirty cycle pulse fed back at point‘D in the diagram. Smoothing out of the general thirty cycle signal pictured in figure D and clipping off of the pip occur in the final filter stage of the generator. 12. Villaire,‘gp..211. -18- D. A. mpur 5.5mm SIGNAL ON CATHODE or 6 0 ~ v1,(ss~ 7) 30~ a. E 5'6““ mozggs OF SIGNAL o~ PLATE or ‘ vyesu) E "355”" vwssu) I9. so ‘ |. SIGNAL o~ CONTROL SIGNAL o~ GRID GRID or vmesm VTs(SSN7) He J0 SIGNAL o~ PLATE SIGNAL on PLATE or or V‘t,(65J7) VTSISSN'H me L. SIGNAL on GRID a PLATE or GLG’s (VT. VT.’) OUTPUT SIGNAL 10, o\~ | 35.30 2.2... l 925 8 so: so... It... i. .. z. «a. A . a , .0 + 5.5:. cohcxmzuu ueo»u 0m be. 0‘8“ .0 4t". E _ Sh<¢0.>..531 8 ooh 2 oh: 800% 0 D3 m; a; I. :.. Ln; 8. 51C o L 23o 2.3M ;