Modern Polymer Spect..

~ polyester
2.6 Alignnient qf Side-Chaiii Liquid- Crystalline Polyrsters 63
film
polarization direction
Figure 2-32. Simplified picture of the experimental
set-up for laser-irradiation and symbolic
representation of the motivation for the
FTIR-spectroscopic detemiinatioii of the order argon.ion laser ,R beam
parameters of the polyester functionalities.
(488 nin)
been studied, but no obvious iinproveinent of the data storage capability 1991 could
be observed.
Thin film of the polyesters were obtained by casting a chloroform solution
(3mg/200 pl) of the polymer onto KBr plates with a 1.5 x 1Oinm' area. After
evaporation of the solvent, the films were dried at room temperature under vacuum
for 2 h. The film thickness obtained by this preparation procedure was approximately
5 pni.
2.6.2 Experimental
Figure 2-32 provides a simplified picture of a laser irradiation/FTIR measurement
experiment symbolizing the inherent problem to determine the laser-induced orientation
of the different polymer segments. The detailed instrumental design of the
apparatus used for these on-line ineasurements is given in Figure 2-33 and shows
that the following experimental parameters can be varied:
0 Based on an internally calibrated photo-diode, the laser intensity can be reduced
from 800 mW/cin2 in a controlled fashion with a neutral-glass filter wheel.
The irradiation time is adjusted by the shutter.
The temperature of the sample is controlled by a Peltier element.
The acquisition of the FTIR polarization spectra is performed by using the
dedicated computer of the spectrometer, which is synchronized with the different
devices. The laser beam passes through the shutter and the filter wheel and is
directed via two mirrors onto the film sample, which is mounted on the Peltier
heater/cooler arrangement. This set-up was used to follow the photo-induced
anisotropy during and after irradiation as a function of time and temperature, as
well as its thermal stability during erasing cycles. Time-resolved spectra with a
resolution of 4 cin-' were taken with radiation polarized alternately parallel and