”H l y (l' L l | I ‘ ‘ l 7 1 | H HI H I HM—l Iowa (hum A STUDY OF MULTI-PHASE LIQUID CRYSTAL BY MEANS OF NUCLEAR MAGNETiC RESONANCE Thesis for the Degree ef M. S. MTCHIGAN STATE COLLEGE Richard D. Ewing 1954 STATE UNNER TY U «Wriumu unnumunniniu‘mfim 93 017014857 . Th to certify that the hesis entitled a J A 4 m - //m of the requirements for & degree in —L0_éfl¢« 00000 PLACE IN RETURN BOX to remove this checkout 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 1/98 campus-m4 A STUDY CF NULTI-PHASE LICUID CRYSTAL U: H: 53 3: Ex»? C3 d1 23 r* on ?’ g1 §. (a ti #3 H c) :J LU U) C) E: (3 91 BY RI CHARD D . E‘~IIT‘IG A THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SC ENCE \l I \a [n ACK‘TO’.‘.'LIJDC—EI>ZEETT I greatly want to thank Professor R.D.Spence for his unhesitating and enthusiastic help in the work behind the preparation of this thesis I am also in great debt to Dr. J.C.Lee for his unselfish assistance in this thesis work more»? 2531310 x \A Table of Contents I Introduction . . , , . . . . . . . . .1. II Dipole-Dipole interaction . . . . . . . . .3. III Apparatus and Procedure . . . . . . . .' IL IV Discussion . _ . . . _ . , , II. Introduction Previous proton magnetic resonance work with compounds of a single liquid phasZ has shown that it is often possible to obtain a unique line shape for the singal of this phase as apposed to those of solid crystalline and liquid phases. Each of these signals consists of a single line - a weckjwide line for the solid crystalline phase while that for the liquid ph se is an extremely strong,narrow line. On the other hand, the signal from the liquid crystal phase in a compound such as para-azoxynisol which has just one liquid crystal phase con- sists of three lines - a rel tively strong’narrow line flanked by two satellibcw lines. A qualitative eXplanation for this line shape is best seen from the structural formula for para-azoxyanisol: A err/300” #0001. The protons in the methyl groups on each end of the molecule con- tribute a triplet shape to the signal, but on this is superimposed a doublet from the protens on the benzens rings along the axis of the molecule. However not all compounds which contribute crystal phases also exhibit unique line shapes for the signals of these phases, but seem- ingly only those which have ethyl, or methyl groups, or both, on the ends of the molecules. In the cases of compounds with ethyl groups CHI the ends, the eXpected signal shape would be one of five peaks - a.}iigh, center peak flanked by two pairs of satellite peakS. 1. However, this thesis is not so much concerned with distinguish- ing the liquid crystal phase as much, but rather with an attempt to distinguish by nuclear magnetic resonance the various liquid crystal phases in compounds which are known to contain several liquid crystal phases, each of these seperate phases by nuclear resonance methods. Specifically, the compound ethylanisal pgga-aminocinnate which has three liquid crystal phaseg was examined in order to determine whether each phase could be distinguished by means of the proton magnetic resonance signal of that particular phase. Chemically, this compound is: O 4’ cysoO—cw = N—O CH =-.. cud From what was mentioned previously, the expected shape for the signal from the liquid crystal phase in general would be a signal of five peaks from the ethyl groug, Superimposed upon a triplet from the methyl group, then these in turn are superimposed upon a doublet from the protons in the benzene rings, and finally the protons along the axis of the molecule will contribute to the center peak. This gener- ally signaled what was found with one qualification which will be ex- plained later. Dipole - Dipole Interaction The classical Hamiltonian for the interaction of two magnetic dipoles in a m:.:gnetic field E is: I . 2/ : fit AIL—- 3 (/(Lpi.4)(4.AL1) ’2} A6" where}4= magnetic moment of the protons 4. = distance between protons of a pair. Then expanding/u" flan/2 in rectangular coordinates with the following relations a; cxxgi = “(9:11; .4131; .4. I35) L1 = .éx 4— £11 + 223 t : I 11619.6 ML»... {ML-TM»- x=3°WW 972' After substitution of these quanlites and some juggline, one finds; in terms of the directinn cosines, a. , 61.1, as . 9v ’: 5%. [gram—.34) + ITI A (—34”) ‘l- 13.1.31 (l~3a:) ~3(Igz‘6. 1.411)](3M79 ”‘3 Consider two non-interacting protons in a magnetic field fig / Then for the Hamiltonian 2 filo :/"’ ”i z X”? (12-, *Iu> Then using the Hamiltonian esan operator in the matrix form and operating on two eigen functions: 9].}:(I). Sd—t.<_o’) 0 A One can write. WOVL‘:E:?SV" where the elements of this diagonalized matrit give directly the 0 energy levels, g? 7‘ )Uszt “‘ "Y‘H23K: However, now consider the same two dipoles only interacting in J" Then it becomes necessary to add the interaction term found previously to H. Th 5, for the total Hamiltonian, HZHo-rH‘ The result of this interaction term is to produce a shift in the energy levels just given. Letzaf: Unperturbed energy leVels Efi': Perturbed energy levels 62: Shift from unperturbed to perturbed energy Similar,llet: (F%3 wave function for perturbed energy levels Hafiz wave function for unperturbed energy levels é . L wave function for shift in energy levels. Then by direct substitution: 0 . . . (Wye/am m) -= (E; +e.><9’. r1.) Assume 9”,. >7 1,550 th. t ya can be ne§_'lected)and ‘since |already know: she’qi.g: 5:2'QL2' then: W ’91. 5E“ 5‘. 90‘- Thus, the problem now becomes one of finding H in diagonal form, so that elements of the diagonal are the shifts of energy levels,dii . Adioint Matrices mm + i a!- th CL C. . ‘. _ . . en 14f:(1r$ Ji‘) MM. To) .. 04 c :. ‘ 1:: ‘ Since, I no i L! 9% (/1- : «29".: then, f I where: $53 =0 4 aid. rv . W‘WWJ'-é¢'$>u =|¢f$=o Theorem: If we have linear operations such tin t e ch operates in Ozlly its own eigen function then: 27% (7:76”) =ZE; (2w) then, for non-interacting protons: Wo t/LLH '3 (”2(15/ 4' 82> l w M ( 0) I . for protons: thenJ ?' 2': LP: (412+ ____5 orientation 1? $1 ‘Pf (P1.— ——9 H “ H 11: - + Ef; t’l9?c 9;. ‘_‘5; H " ” l'T ngguu'ky; __, H .. .. H II However, to insure that H is diagonalized it is better to usg: E‘ 1 El). 1E2.:: ;é;(\SP11*- SEE?) 323’:. é§_(}izl - 99g?) 331,-. #419" Now have: EJWIQ = éé W" %2(Im120(3m26~‘> __ 15.325 [(11.4 ryxrmmrn) ‘11:} + (In +8],- ,)(Ix1-L‘I‘11‘)](3wze'l> at“: g g . (M ‘ I, +813 ‘M-l) 2 V(I,.M)(I.M+g) (m lI;-— dual/w) = VYr-MMLZB CM» [Iii/M.» 1‘— M Consider 1+Wlig= 6!, E: (I,.1',,3§ :e. a» 13*.ch,.‘£,,)§ W» (@123qu s: "' Lie-((Em 9-13 L995 EILEEIVQE, = - é,‘= ~3L§(u:<:‘e 0 (c) a; (la. I223 E, = - '- 6,’ = 4' Xi‘L‘bmqe-A 4.12.3 as Haggai, a -;1, $3,: *- fl:(3m?O—l\ a I Lu -cI ML,“ an] E m3 1|[(Ixt-LI:1!3(IX1+LI“I)] - 0 3 6!, as am a. «11pm. + c‘Ipflr- o= €v (63 £3 [L Ix. ‘ €L~1l>(Ix-fi " I11>11i e: : 2%. (arm‘s—:3 . =_l (£3 E: {th."‘—I‘3I)(Ix1+‘-I“stfl l 1. 'L 6.; : Xg/fi3(3w26_“) 3. I: [LIx.+“-T~b‘)(rxz' (114.60] £5 a» 3? [(1,012 LAME”; 6 Lbs] E. —— o -. e,” “IA E: [LIX\+L‘I“6(\LI11‘ [1117)] EH 3 O 1 6%”, . \ K'B E: [(1)0 +L‘. [~33(IK‘L~ C ['15)];2 :— .2 62m: Y%:(3 w29~ I) l d» E:[LIX‘+ (:IITBLIX’L“ ('Idj131‘E-5: -3. 63'." :_Y"fi 2 Co, SC": M1643 J), Thus, for the shifts to the perturbed energy levels, -e ‘.e ".e’”— —1_.1 (3,0,9 ,3- — 7,6»:‘(3u4w-0 61-6;+€{’+6"’ :+ 2%C3W19‘ -1) 7. 49/4, 114(30-029‘0 é‘l 36‘; *64'*e‘t”"= ‘ $(3m‘é—I) 2-,u12,"3(30429“’) ’53 = O Resonance absorption then occur for the perturbed system when5 M:+l—~M.=. o A"): 9/4/79 * 3/czh‘3(30429 -I> M20 qm=-l m = Q/qu -s/;‘a“(sm=e—l3 M: 2/1 H" Jhere ffiis the resonance field value Substitute: H’s/1’, tcx(3m26~¢) where —2 0(2 ”R. we Thus, the energy level diagram showing the effect of the per- turbing dipole - dipole interaction on the unperturbed levels \ \ W"—: 2/4. H; yeti-3 (scu‘e- I) 1’9=?/~Hg-3/¢921£3(3w'6~l3 e_ 1. -'s z _ // W - 9/041}. (3w 6 l) figs) -_ Q/LLHE r Sjpzn-s(‘$ “42$ ‘43 K \ \__ __ W.“ 2 Q/Lghla —/tc2/2'3('5w26“/§ lo. Apparatus In the detection of the signal, the apparatus used is essentially the same as the radio-frequency bridge method discussed by Villaireg. The l ne widths are then measured with the sa e method and accuracy as was done by Moses. Discussion In the attempt to dectect licuid crystal phases, the compound ethyl anisal para- aminocinnamate was used. According to the optical observations of Bernal and Crowfoot this compound possesses three liquid crystal phases, with the transition temperatures as indicated in the following diagram. . MI I§°Id Wages; W Eggs WIT ’a iilJar -r”72;;;13 (We) As was stated before, the expected signal from the liquid crystal phases would consist of five peaks. However.the actual signal found for all the liquid crystal phases was of the form shown in figure I II. The apparent absence of two satellite peaks here is in accord with previous experimental results which have shown that' molecules with a methyl group on one end and an ethyl group on the other two of the satellites are masked so that the overall picture is simply a triplet. Before continuing, it should be pointed out that the compound used appeared to be impure. This was derermined by merely visually observing the various phase transitions for a small sample in a temp- erature bath. It was found that each transition occurred about 1-40 c lower than the respective transitions indicated by Bernal and Crowfoot} However, it seemed to exhibit enough line structure and be sufficiently pure to warrant going ahead with tge work. In order to detect these various liquid crystal phases, the satellite peak separation of a signal was measured as a function of temperature. These peak separations were then plotted versus temp- erature,.and granh#l'was obtained. Here the peak separation is measured in guass and the temperature in degrees centrigrade. In this graph there appears to be three very distinct portions which are taken to be the magnitude of the satellite peak separation in each of the three liquid crystal phases. The portion of the curve at the right which slopes rapidly up from the liquid phases is taken to be the first licuid crystal phase. The satellite peak separations here vary from.l.2 guass atl§l.2 0c, which is close to the clear point,UP to the 5.4 gaass at 1170c. IZD Gov mmakdmmn—ZMF on. e: on. . em. 0: 09 em 8 oh i . _ _ _ _ _ _ o._ 1 o.~ .. o.» . _ _ .. oé _ “ mndzqm cum: 4 _ Basie :mmma o u 1 on _ . 4 d _ 2.25 e I 0.0 4 d NOIlVHVdBS )IVSd Bil-I‘IBLVS (SSHVO) OS _ Om— . 1 I ON. . {Mn «0.; mmnbdmeZMF o: 00— om . . . V) /i\ mun—41m wz... The two lines of this section seem to indicate some decom- position in the compound upon successive beatings. The line drawn through the circles represents a sample of which the data was obtained upon the first heating, while the line through the triangles represents the same sample after it has been heated previously. And while the results shown here are not sufficient to positively state that a trend is established as shown, that is, successive heatings decompose the compound in such a manner as to produce lower satellite peak separations in the first liquid crystal phase, still it is the opinion of the author that this as so, especially since it was found by visual observations that the clear point was lowered by as much as 1500. upon many heatings. The exact cause of this decomposition is not known. The second section of the curve from 1170c. down to 1080 repre- sents the second liquid crystal phase and here the satellite peak separation remains constant at 5.4 guass. It should be noted here that the transition from the first to the second liquid crystal phase is represented as merely the change in slope of the curve. This is in qualitative agreement with the observations of Bernal and Crowfoot} who state that there is but a small difference in the optical behavior of these two phases, then at 105°C. a sharp discontinuty occurs and there is a sudden increase in peak separation. This third portion of the curve then is taken to represent the third liomid crystal phase and here the peak separations vary from 5.8 guass at 1050c to 6.8 guass at 800C. Thus, these transitions appear to agree with those of IR. Bernal and Crowfoot as well as could be expedted considering the purity of the sample. The next graph shows the change in shape of the signal with temperature. Each of the three peaked signals represents the three liquid crystal phases, while the single peak at the extreme right is the signal of the liquid phase. An interesting feature of this com- pound is that while it is heated it appears to go from a solid cryst— alline phase with its charasteristic broad line into a second metast- able solid crystalline phase with the same type signal only with a spike on top. From here it passes into the second liquid crystal phase and then into the first and after that into the licuidphase. 6n cooling, however, it traces back along through the first and second liquid crystal phases, b t then it dumps into the third liquid phase at 10500. But it is not at all positive that here the compound is all in the third liquid crystal phase, but rather it is possible that, as Bernal and Crowfoot indicate there is a coexistance of both this liquid crystalphase and the metastable crystalline phase. We point at which the compound passes from the third liquid crystal phase into the solid crystalline phase was not determined due to the difficultyy in obtaining a workable signal pastBOOc. Thus, from these results it appears to have been possible to detect all the general features of the various phase transitions which were found by Bernal and Crowfoot by Optical observations. / V/ Literature Cited J.D.Bernal & Crowfoot, Crystalline Phases of some Substances studied as Liquid Crystals, Discussion held by The Faraday Society, April (1955). N. Bloembergen, Nuclear Magnetic Relaxation Martinus Nijhoff, (1943). pp.12, 55-54. P.L.Jain, Proton Resonance in Nematic Liquid Crystals, Ph.D. Thesis, Michigan State College,(1954) H.A.MOSes, The Proton Resonance Absorption in Liouid Crystals, thters Thesis, Michigan State College (19533; G.E.Pake, Nuclear Resonance Absorbption ig_Hydrated Crystals: Fine Structure 2: the Proton Lin1,Journal of Chemical Physics, 35. 527 (1948). r L.I.Schiff, Quanturn Mechanics, McGraw-Hill Book Co.,(l949). R.D. Spence, H.A. Hoses, P.L. Jain, The Proton hagnetic Resonance in Liouid Crystals, "Journal of Chemical Phisics, February,195§,pp208. J.H. Van Vleck, Dipolar Broadening g: magnetic Resonance Lines in Chrystals, Phisical Reveiw, Zfl, 1168,(l948). 15’.- llillfllllllllIll!"Hill”lulllllflfllfllMINIMUMIINHI 017014857