Liquid crystal comb polymer with polar mesogenic and aliphatic side groups II. Noise of the scattered light

Abstract

Measurements of static light scattering and of the stationary noise of the scattered light have been performed as functions of temperature on the comb polymer whose synthesis and static structural properties are discussed in the preceding paper, Part I. The intrinsic optical noise strongly increases when the nematic phase is entered. An additional maximum in the noise, observed at lower temperatures, is attributed to a rearrangement of optical domains, introducing boundary regions where the fluctuations of loosely packed side groups are enhanced. The spectral density of the observed noise is definitely non-Lorentzian and can be fitted by the superposition of two pure Lorentzian components with different cut-off frequencies, attributed to the statistically independent random motion of mesogenic and aliphatic side chains. The noise level is reduced at all temperatures by an applied electrical field; in particular, the field is effective in selectively damping the fluctuations of polar side groups.