# Two dimensional correlation spectroscopy applications in vibratioal and optical spectroscopy - Isao N.

ISBN 0-471-62391-1

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2 $ 1434, 1307) > 0 ^ (1434, 1307) > 0 1434 cm- before 1307 cm-1

3 $ 1307, 1064) < 0 ^ (1307, 1064) > 0 1307 cm- after 1064 cm-1

4 $ 1461, 1415) > 0 ^ (1461, 1415) > 0 1461 cm-1 before 1415 cm-1

5 $ 1446, 1430) > 0 ^ (1446, 1430) < 0 1446 cm-1 after 1430 cm-1

6 $ (1446, 1079) > 0 ^ (1446, 1079) < 0 1446 cm-1 after 1079 cm-1

7 $ (1430, 1126) < 0 ^ (1430, 1126) < 0 1430 cm-1 before 1126 cm-1

8 $ 1380, 1126) < 0 ^ (1380, 1126) < 0 1380 cm- before 1126 cm-1

9 $ 1438, 1130) > 0 ^ (1438, 1130) > 0 1438 cm-1 before 1130 cm-1

10 $ 1438, 1060) > 0 ^ (1438, 1060) > 0 1438 cm-1 before 1060 cm-1

11 $ 1419, 1130) > 0 ^ (1419, 1130) > 0 1419 cm-1 before 1130 cm-1

12 $ 1419, 1060) > 0 ^ (1419, 1060) > 0 1419 cm-1 before 1060 cm-1

13 $ 1419, 1295) > 0 ^ (1419, 1295) > 0 1419 cm-1 before 1295 cm-1

14 $ 1461, 1295) > 0 ^ (1461, 1295) < 0 1461 cm-1 after 1295 cm-1

15 $ 1461, 1130) > 0 ^ (1461, 1130) < 0 1461 cm-1 after 1130 cm-1

16 $ 1461, 1060) > 0 ^ (1461, 1060) < 0 1461 cm-1 after 1060 cm-1

17 $ 1419, 1130) > 0 ^ (1419, 1130) > 0 1419 cm-1 before 1130 cm-1

18 $ 1419, 1060) > 0 ^ (1419, 1060) > 0 1419 cm-1 before 1060 cm-1

“ Vj after (before) V2 means the intensity change of the band at u occurs at higher (lower) VA contents than that at U2.

orthorhombic crystalline phase. The all-trans bands at 1130 and 1060 cm-1 have positive synchronous correlation with the crystalline band at 1415 cm-1, negative correlation with the amorphous band at 1307 cm-1, and negative correlation with the anisotropic bands at 1446 and 1434 cm-1. This observation indicates that the amount of all-trans chains in EVA copolymers is reduced with an increase in the VA content. It was also revealed from Figure 10.22 that various gauche conformations appear with the incorporation of VA comonomers. One should notice here that the structural variations induced by the change in the VA content of only 2wt% are clearly detected in the 2D Raman correlation maps.24

Set 2 contains three EVA copolymers with somewhat higher VA contents of 10, 15 and 20wt%. Figure 10.23(A) and (B) shows synchronous and asynchronous correlation spectra for Set 2 in the region 1500-1200 cm-1.24 A band at 1380 cm-1 is assigned to the CH3 symmetric bending mode of the acetate groups. It has negative correlation with the crystalline band at 1415 cm-1 and the all-trans band at 1295 cm-1, indicating that with the inclusion of VA comonomer the crystallinity of EVA decreases, and the population of all-trans conformers reduces. A band at 1461 cm-1 has been assigned to the first overtone of CH2 in-phase rocking mode at 730 cm-1, which is characteristic of the -(CH2)-n structure for n > 3 in the crystalline phase.44 This band shares positive cross peaks with the crystalline band at 1415 cm-1, implying the shortening of CH2 sequences. Moreover, the band at 1461 cm-1 has an asynchronous relationship

208

Generalized 2D Correlation Studies of Polymers and Liquid Crystals

Wavenumber/cm 1, v1

Figure 10.22 Synchronous 2D Raman correlation spectrum in the region of 1500-1200 cm-1 and 1200-1000 cm-1 for EVA copolymers with VA from 6 to 8wt%. (Reproduced with permission from Ref. No. 24. Copyright (1999) American Chemical Society.)

Figure 10.23 (A) Synchronous 2D Raman correlation spectrum in the 1500-1200 cm-1

region for EVA copolymers with VA from 10 to 20wt%. (B) The corresponding asynchronous correlation spectrum. (Reproduced with permission from Ref. No. 24. Copyright (1999) American Chemical Society.)

2D IR Study of Ferroelectric Liquid Crystals

209

with the band at 1415 cm-1 (Figure 10.23). The fourth row of Table 10.3 shows that the event at 1461 cm-1 occurs before that at 1415 cm-1, indicating that the shortening of contiguous CH2 sequences takes place prior to the shrinking of crystalline lamellae with the increase in the VA content.

Using the same 2D correlation analysis method, Ren et at.24 reached the following conclusions for Set 3 and Set 4. Set 3 contains EVA with middle level VA contents from 25, 26, and 28wt%. The main event for Set 3 is the shortening of all-trans CH2 sequences, which reduces the correlation splittings of the crystalline phase. The crystalline packing in the unit cell deforms first, and then the CH2 segment in the unit cell loses its all-trans conformation. Set 4 contains EVA with high level VA contents from 28, 32, and 42wt%. The main event for Set 4 is the further shortening of the all-trans CH2 sequences, resulting in the deformation of the orthorhombic unit cell. The anisotropic phase loses its lateral order for Set 4.

10.5 POLARIZATION ANGLE-DEPENDENT 2D IR STUDY OF FERROELECTRIC LIQUID CRYSTALS

The next example deals with an interesting 2D IR correlation study of the spatial or orientational distribution of constituents in a liquid crystal sample. Ferroelectric liquid crystals (FLCs) have received keen interest as the most recent member of the family of ferroelectric materials because of their potential applications in high definition, flat panel displays, and optical processing devices.45 46 For FLCs in the Sm-C* phase, a very thin (only a few ^m) cell is used to take advantage of the boundary condition imposed by the orientation layers, which is strong enough to suppress the formation of a helix. This effect is called the surface-stabilized ferroelectric liquid crystal (SSFLC) effects. By reversing the polarity of the applied electric field, molecules can be switched back and forth from one state to the other state at a fast speed in the microsecond range.

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