Modern Polymer Spect..

2.5 Electric Field-Im/irced Orientutioii 49
I
- 1 ' I I I I
32OU 3000 2750 2500 2250 2000 1750 1500 1250 I000 750 500
WAVENUMBER / cm'
Figure 2-15. FTIR polarization spectra of NLCP (25 "C) taken with radiation polarized parallel
and perpendicular to the rubbing direction.
groups. With the development of this formalism it is now possible to construct 2D
correlation plots based on conventional time-resolved spectral data. The 3D analysis
reveals [ 161, that there is a strong correlation in the synchronous spectrum and
no appreciable asynchronicity in the asynchronous spectrum between the niesogen
bands and the absorptions of the hydrocarbon chain (see Table 2-1). This means,
that the mesogen and the flexible segment of the liquid crystal reorient synchronously.
The strong correlation between the inesogen bands themselves indicates
that the mesogen reorients as a rigid core. No differences in 2D correlation spectra
between the orientation and relaxation processes were found.
2.5.3.2 Nematic Side-Chain Liquid-Crystalline Polymer in a
Switching Experiment
The FTIR polarization spectra of the prealigned NLCP are presented in Figure
2-15. Due to the almost identical structure of the side-chain compared with the lowmolecular
weight liquid crystal (6CPB), most of the functionality-specific band
assignments of Table 2-1 are also valid for the NLCP. The 1603 c1n-l and 1503
cm-I (phenyl C=C-stretching vibrations) bands and the 2230 cm-' (v(C_N)) band
are polarized along the long axis of the mesogenic functionality and show parallel
dichroisni with All > AL. This means, that the long axis of the mesogenic unit is
predominantly oriented parallel to the rubbing direction. The 757 cni- ' bund (ring
CH out-of-plane deformation) exhibits a perpendicular dichroisni with Al > All
because the transition moment for this band is perpendicular to the ring plane and
hence, perpendicular to the long axis of the mesogen. Since the transition moment