Quasielastic Light Scattering from Orientational Fluctuations in a Cholesteric Liquid Crystal

Abstract

Examination of the Rayleigh line of a lyotropic cholesteric polypeptide liquid crystal by the techniques of quasielastic light scattering spectroscopy reveals the presence of two new purely dissipative low frequency light scattering modes of comparable intensity. Angular and electric field dependences of the deconvoluted spectra are consistent with the identification of the mechanism as due to twist and viscous-splay normal modes recently predicted theoretically. Analysis of the narrow mode on this basis yields a value of γ₁, the twist viscosity coefficient of the medium. The broader mode results in an estimate of the value of the ratio of the splay to bend elastic moduli, K ₁₁/K ₃₃ ∼ 10⁻⁵, which is shown to be in accord weith mean field theoretical calculations for a system of such highly elongated macromolecules.