TEMPERATURE BEHAVIOR OF A LIQUID-CRYSTAL COMB POLYMER - LIGHT-SCATTERING AND NOISE OF THE SCATTERED-LIGHT

Measurements of the intensity of the monochromatic light transmitted t hrough and scattered by a comb polymer with a polyacrylamide main chai n were performed between room temperature and the isotropization tempe rature of the polymer. The stationary noise of the light scattered at low angle was measured in the same temperature interval. The transmitt ed intensity is observed to increase strongly above the smectic S-I2-S -C2 transition, where the intensity of the light scattered at low angl es is maximized. The power dissipated by the molecular fluctuations dr amatically increases above the transition between the two smectic phas es. The spectral density curves display a Lorentzian character only be low the S-I2-S-C2 transition. At higher temperatures, a more complex f requency behaviour of the stationary noise spectra is observed. Such a behaviour is interpreted in terms of a model explicitly invoking the effect of the Brownian movement of segments of the main chain (backbon e) of the polymer on the side chain fluctuations. The parameters gover ning the Brownian movements of both main and side chains, and their ev olution with temperature, are determined and discussed in the light of a simple structural model.