Modern Polymer Spect..

54 2 Segmental Mobility qf Liquid Cyvstrrls cmd Licliiid-Cvystalliiie Po1jwer.r
I
I
3000 2400 is00 1200 600
WAVENUMBER /[ cm-']
Figure 2-20. Step-scan FTIR spectra of the investigated nematic liquid-crystalline guest-host
solution before (0.0 ms) and after (19.5 ms) reorientation in the electric field.
0.
L
2 0.
4
B
I
0 10 20 30 40 so
Figure 2-21. Relative absorbance changes versus time of the v,(CH?) (0) and v(C=N) fV) nbsorption
bands of the solvent and the solute-specific v(C=O) (0) band during orientation and relaxation
of the individual segments.
tive absorbance of the v(C-N) relative to the v(C=O) band are due to two effects:
(1) better initial orienation in the rubbing direction; and (7) the more eficient
reorientation of the C-N functionality into the electric field direction.
The positive values for the relative absorbance of the vs(CH2) absorption reflect
the preferential perpendicular alignment of the transition moiiieiit direction of this
band relative to the long axis of the nematic solvent molecule. A recent study 1291