OPTICAL NOISE AND DYNAMICAL PROPERTIES OF LIQUID-CRYSTAL COMB POLYMERS WITH DIFFERENT MESOGENIC GROUPS

The light scattered by a comb polymer with a polyacrylamide main chain and biphenyl-based mesogenic units containing the substituent R = CN in the biphenyl core is characterized by a stationary noise which has been measured between 70 degrees C and 140 degrees C in the frequency interval 5 x 10(-2) less than or equal to v less than or equal to 10 H z. This optical noise is analysed by means of a specific procedure int roduced to clarify the role of random movements of segments of the mai n chains on the side chain fluctuations. The RMS amplitude of the rand om molecular movements, the relaxation times of the side chain and mai n chain fluctuations, and the damping coefficients governing their mot ion are investigated as functions of temperature. The results are comp ared with those recently obtained on a similar polymer characterized b y R = H. Common features and differences are brought into evidence and discussed in terms of the different mesophase structures exhibited by the two polymers in the temperature interval considered.