Electro—Optic and Dielectric Studies in Cholesteric Liquid Crystal Mixtures

Abstract

In binary mixtures of cholesteryl chloride and cholesteryl alkanoates, the threshold field for the cholesteric to nematic transformation depends on the length of the alkanoate ester chain. The threshold field also depends on the pitch, the dielectric anisotropy and the twist elastic constant of the mixtures. This paper describes the experiments performed to establish the role of these three parameters in the observed variation of threshold field with alkanoate ester chain length in such binary mixtures.

The temperature dependence of threshold field, dielectric anisotropy and pitch has been studied. From these experiments the relative response of the various mixtures to applied electric fields has been established. In most of the mixtures, temperature ranges over which pretransitional effects do not predominate, have been identified. Twist elastic constants of the mixtures in these temperature ranges have been calculated. It has been shown that both the intrinsic response of the mixtures to applied electric fields, and the twist elastic constants do not show a regular variation with chain length of the alkanoate ester tail. Some observations suggest that mixtures containing non-smectogenic alkanoates show different temperature dependence of threshold field as compared to those containing smectogenic alkanoates.