Modern Polymer Spect..

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induced alignment of the investigated polyester and the following scenario is suggested for optical storage: the film obtained by casting from solution consists of' macroscopically isotropic niicro-domains. The irradiation with linearly polarized laser light leads to a melting of these domains, caused by direct heating due to absorption or a deposition of heat through traris-cis-trms isonierization cycles of the azobenzeiie moieties [95]. The origin of the orientation effect is attributed to tivm,r-cis photoisomerization of the azo-group, followed by a c-is-trans thermal or photoisomerization. In the cis-form, this functionality is able to undergo some reorientation with respect to its original alignment. The absorption of the polarized 'writing' beam will continue as long as a component of the electric dipole vector of the azo-group lies in the direction of the laser polarization. The trurzs-cis reorientation process will therefore continue until all the azo-groups have been oriented perpendicular to the polarization vector of the laser beam [86. 1011. In the polyesters investigated here, this orientation remains after the 'writing' beam is turned off and a long-tenn stable, macroscopic orientation is established. Apart from this long-term stability, the possibility to erase and reinduce this anisotropy in the polymer is a prerequisite for its application as a reversible optical data-storage medium. To demonstrate the loss of mesogen-alignment during heating and the perfect reversibility of a 'write-erase-write' cycle, Figure 2-37a shows a stack plot of the i(C-N)-band region in the polarization spectra of a P10a12 film during heating from 32 "C to 100 "C (isotropization temperature, 68 "C) and in Figure 2-37b the dichroism of the v(C-N)-band of the same polymer is shown (from left to right) after irradiation, upon heating the irradiated sample to 100°C and after reirradiation. The aliiiost perfect coincidence of repeated writing cycles is demonstrated in more detail in Figure 2-38a, which displays the simultaneous photo-induced alignment of the different segments during laser irradiation in an order parameter/tinie-plot. Figure 2-38b exhibits the intermediate thermal erasure of the first orientation as a function of temperature. The loss of orientation for the different polymeric segments is also coupled and takes place in a narrow teniperature interval. A comparison of Figure 2-38b with the transition temperature ranges of the individual phases in Table 2-2 shows that, during erasure, the anisotropy is mainly retained in the less ordered mesophases 3 and 4. Beyond 54 "C, only a small, residual anisotropy is observed due to recrystallization effects [96], which completely disappears at the clearing point of phase 2. 2.7 Orientation of Liquid Crystals Under Mechanical Forces Apart from the orientation mechanisms discussed in the previous sections, a preferential alignment of liquid crystals or liquid-crystalline polymers may also bc induced by the application of mechanical forces. Depending on the investigated system, this can be either done by shearing between plates or in stress-strain niea-
100 “C 2300 2200 2100 walenumbers [cm-’] I00 “C 2300 2200 2100 wavenumbers [cm-11 1 e 2 0 0.20- z - 4 80 wavenumbers [cm-l J Figure 2-37. Thermal erasure of a laser-induced alignment in a PlOal2 polyester demonstrated by the disappearance of the v(C=N) dichroism at the isotropization point (68°C) (a) and the effect of irradiation, thermal erasure and reirradiation on the v(C-N) dichroism of the same polymer (b). surements of bulk samples [36, 102-1041. <strong>Spect</strong>roscopic data on the orientation induced by these pretreatments may then be utilized for a better understanding of the different responses of specific functionalities to the external force field, or they can establish the basis for a correlation of the mechanical properties and the structure of the liquid-crystalline system.
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Modern Polymer Spectroscopy Edited
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Modern Polymer Spectroscopy Edited
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Preface For unfortunate reasons the
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However, theory and calculations yi
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Contents 1 Two-Dimensional Infrared
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Con ten t~ xi Index 5.2 Force Field
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Contributors M. Del Zoppo Dipartime
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1 Two-Dimensional Infrared (2D IR)
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1.2 Brick~qrorrnrl 3 . Figure 1-3.
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1.0 , Figure 1-6. The in-phtrse and
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1.2 Bcrckgroinizd 7 where AA (i~) i
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1.2 Background 9 1.2.5 Two-Dimensio
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1.3 Bnsic Properties of 20 IR Corre
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2D IR spectrometer coupled with a d
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1.5 Applirtrtions 15 Unlike a dispe
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Page 34 and 35: 11 Amorphous Crystalline ,...." I F
Page 36 and 37: 1.5 Applications 21 / I 1430 Figure
Page 38 and 39: 1.5 Appliccitioiis 23 Methylene Fig
Page 40 and 41: 1.5 Ajqdicrrtions 25 3024 Figure 1-
Page 42 and 43: 1.5 Applicutions 27 Furthermore. th
Page 44 and 45: 1.7 Coizclirsions 29 derived in a s
Page 46 and 47: 1.9 References 31 [9] Colthup, N. B
Page 48 and 49: 2 Segmental Mobility of Liquid Crys
Page 50 and 51: SRMPLE/DETECTOR e3 ‘retardation
Page 52 and 53: 2.4 Srvuc me-Dependenr Alignment 37
Page 54 and 55: 2.5 Electric Field-Innductid Orirnt
Page 56 and 57: 2.5 Electric Field-nclticetl Orient
Page 58 and 59: a -@ COWER SRHPLE ._ 2.5 Elec tric
Page 60 and 61: 2.5 Electric Field-Itzduced Orienta
Page 62 and 63: 2.5 Electric Field-IwrElrced Orient
Page 64 and 65: 2.5 Electric Field-Im/irced Orientu
Page 66 and 67: 2.5 Electric Field-Induced Orientli
Page 68 and 69: 2.5 Electric Field-Induced Orientat
Page 70 and 71: 2.5 Electric Field-Induced Orienfat
Page 72 and 73: 2.5 Elrc tric Field-Iiidircwl Orim
Page 74 and 75: 2500 2008 I s00 WRVtNdMRtR CM-I Fig
Page 76 and 77: -3.6 Aligmient OJ' Side- Clinin Liy
Page 78 and 79: ~ polyester 2.6 Alignnient qf Side-
Page 80 and 81: I." 0.9 0.8 Figure 2-34. FTlR 0.7 p
Page 84 and 85: 2.7 Orientation oj Liquid Ci:i,stal
Page 86 and 87: 2.7 Orieritation of Liquid Ciysttrl
Page 88 and 89: 0 8 18 16 1 a W u z a m a 0 Ln m Q
Page 90 and 91: 2.7 Orientation oj Liquid Crystals
Page 92 and 93: 2.7 Orientation of Liquid Crjvtals
Page 94 and 95: 2.7 Orientatioiz of Liquid Crystals
Page 96 and 97: 2.8 Conclusions 81 strain. As A0 is
Page 98 and 99: 3. I0 Refcreiice.r 83 [I 71 Hoffina
Page 100 and 101: 2.10 References 85 [92] Wiesner, U.
Page 102 and 103: t Order/Disorder in Chain Molecules
Page 104 and 105: onds which hold atoms together thro
Page 106 and 107: 3.2 The Dyriamical Case qf Simll ar
Page 108 and 109: 3.2 The Dyrinniical Case of Sinnll
Page 110 and 111: 3.4 S11or.f- and Loizg-Rcrizye Vibr
Page 112 and 113: 3.4 Slzort- and Loiig-Range Vibrati
Page 114 and 115: eyularity), e.g., 2. During the pol
Page 116 and 117: 3.5 Towards Lnrger Molecules: From
Page 118 and 119: 3.5 TOIIYW~ Laiyer Molertiles: Fvoi
Page 120 and 121: 3.5 Towmu" Larger Molecules: F~om O
Page 122 and 123: 1700 - CIO --- ca c 22 _- c 12 l l
Page 124 and 125: 3.6 From Dynamics to Vibrational Sp
Page 126 and 127: 3.6 Froin Dynaiiiics to T’ihratio
Page 128 and 129: 3.7 The Case of Isotactic Polypropy
Page 130 and 131: 3.7 The Cuse of Isotactic Polypvop.
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3.8 Density of Vibrational States a
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3.8 Dtvz.sit,v of L’ihrntioizal S
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3.8 Driisity of Vibratioiid StLitrs
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3 9 Mouiiiq ToIvmds Rerrlitv: From
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3.9 Moving Towards Reality: From Or
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3.9 Moving Towards Reality: Froin O
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3.10 Wlmt Do We Learn from Cnlcailc
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+ 3.11 A Very Siriiple Ccrse: Latti
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3 I1 A Yey) Siiiiple Case: LLittice
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3.11 A Vq> Siiiiplc Crrw: Luttice D
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Figure 3-22. Sample eigenvectors in
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3.12 CIS-trans Opening @the Double
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3.13 Defect Modes cis Structtrr.al
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3.13 Defect Mo&s cis Structurcil Pr
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0 3.14 Case Studies N 0 d - Y N o m
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3.14 Case Studies 147 OC 60 58 57.
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3.14 Case Studies 149 GI A V E N U
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3.14 Case Studies 15 1 correspond t
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3.14 Case Studies 153 (I10 + 200) +
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3.14 Case Studies 155 1500 1480 146
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3.14 Case Studies 157 the molecular
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17E (ir 1, R): (iii) z = 4, t = 1,
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3.16 Stnictural Znlioi~zogeneity an
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3.1 7 Fermi Resonancrs 163 stants.
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3.1 7 Femi Resorinnces 165 2 L 1 29
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lowing. The CHl-bending mode 6 [cer
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3.17 Ferini Re.sonrriire.s 169 a Fi
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3. I7 Fernii Resoiiances 17 1 terin
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3.18 Band Broadening and Confonnati
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3.18 Bmd Brourleiziriy md Cmforrnat
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3.18 Band Bvoaderiing arid Conjonna
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3.18 Band Broadening and Confornmti
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3.19 A Worked E.utinple 181 pre-mel
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3.19 A Wovh-ecl E.uanzple 183
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3.19 A Worked Example 185 19 5°C 2
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3.19 A Workrd Example 187 Figure 3-
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3.19 A Worked E.rcnniplr 189 LAM I
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3.19 A Worked E.xuniple 191 Figure
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3.19 A Worked E.vnn~yle 193 Figure
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3.19 A Worked E.vnrqde 195 009.1 00
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3.19 A Worked Example 197 existence
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3.1 9 A Worked Example 199 The soli
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3.20 References 201 very important,
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3.20 References 203 [41] M. Gussoni
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3.20 Refeeveiicrs 205 [I 171 P. Jon
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4 Vibrational Spectroscopy of Intac
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4.3 Georrietvy oj Intuct Po1vniev.r
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1'45 4.4 Geometric Chunges I?zditce
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4.4 Geometric Chmges Iiid~lrcecl bj
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4 5 Mer1iodolog.v of Raiii~11 Studi
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4.7 Poly(p-pheiq.lene) 217 with an
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4.7 Pol)~(p-pheiz~~lene) 219 ENERGY
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is worthwhile pointing out that the
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~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 801 Table 4-3
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4.7 Poly(y-phenylene) 225 Figure 4-
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Table 4-4. Observed Raman frequenci
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4.8 Other Polwieys 229 Table 4-5. T
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under various models. According to
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4. I0 Mechnriism oj Charge. Transpo
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4.12 Reftrences 235 [ 131 Kuzmany,
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4.12 References 237 [98j Matsunuma,
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5 Vibrational Spectroscopy of Polyp
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5.2 FOYCC Fields 241 such calculati
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5.2 Force Fields 243 accounts for o
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5.2 Force Fields 245 centers of the
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5.2 Force Fields 247 ture with conf
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5.3 Amide Modes 249 to the nh initi
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5.3 Ainide Modes 251 Table 5-1. Ami
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Table 5-2. Some amide modes of four
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5.3 Amidc Modes 255 Figure 5-1. Opt
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5.4 Polypeptides 257 nonhydrogen-bo
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5.4 Polvpeptida 259 Figure 5-2. Ant
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I 5.4 Polypeptides 261 )I .- + $ 80
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1226M 1222s (1 1165W 1167s (1 1120V
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135s 9 1 Ms1i 122Wbr 147 NH ob(37)
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5.4 Polypeptides 267 glycine residu
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5.4 Polypeptides 269 Raman bands in
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5.4 Polypeptides 271 Figure 5-7. St
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Frequency (cm-'1 100% b 700 500 300
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5.4 Polypptidt~s 215 Table 5-9. Obs
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~~ ~~ ~~~ ~ ~ ~~ 5.4 Polypeptides 2
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5.4 Poliyeptides 219 Table 5-11. Co
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Table 5-12. Aniide mode frequencies
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1351 Lifson, S., Stern, P. S., J. C
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5.6 Refeverices 285 [130] Tiffany,
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Index Amide modes 249 Amorphous pol
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Step-scan FTIR spectroscopy 14,34 -
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