Modern Polymer Spect..

2.7 Orientation oj Liquid Ci:i,stals Under Mechanicul Forces 69
a
b
solid symbol 1st writing cycle, open symbol 6th wntlng cycle
1 ' 1 9 I , I I I ' I
0 200 400 600 800 1000 30 35 40 45 50 55 60 65 70 75 80
Irradiation time Is Temperature I "C
Figure 2-38. Reversibility of repeated write/erase-cycles demonstrated in time-resolved FTIR
polarization measurements by the order parameter for the different segments of PSal?: (a) As a
function of irradiation time (488 nm line of an argon-ion laser, at 30"C, SOOmW/cm') in the 1st
and 6th cycle; and (b) Versus temperature during thermal erasure with a heating rate of 30 "C/niin.
2.7.1 Shear-Induced Orientation in Side-Chain Liquid-Crystalline
Copolysiloxanes
As pointed out already in Section 2.5.5, low-molecular weight ferroelectric liquid
crystals (FLCs) and FLCPs are attracting a lot of interest because of their potential
for electro-optical applications. The polymers offer new possibilities, e.g., as elastomers
for piezoelectric elements or by copolymerization [77, 78, 1051 due to the
formation of intrinsic mixtures between SniCY' mesogenic units and other coinonomers.
This leads to FLCPs combining several material properties which might be
utilized for colored displays in the case of comonomers containing chi-omophores.
For the differentiated evaluation of such copolymers with reference to the possible
exploitation of nonlinear optical (NLO) properties, the interplay of the different orientation
tendencies of the side-chain functionalities is of crucial importance [36, 1061.
2.7.1.1 Materials
The copolymers presented here are copolysiloxanes whose liquid-crystalline phase
behavior is characterized by the formation of a SmC* phase. By the additional