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 Hz. This optical noise is analysed by means of a specific procedure introduced to clarify the role of random movements of segments of the main chains on the side chain fluctuations. The RMS amplitude of the random molecular movements, the relaxation times of the side chain and main chain fluctuations, and the damping coefficients governing their motion are investigated as functions of temperature. The results are compared with those recently obtained on a similar polymer characterized by 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.