Circular dichroism in absorbing mixtures of right- and left-handed cholesterics

Abstract

A rigorous theory of the optical properties of absorbing mixtures of left and right handed cholesteric liquid crystals has been developed. Detailed expressions and illustrative calculations of the dependence of circular dichroism on pitch and sample thickness are presented. Experimental studies have been carried out on a 1.64:1 (by weight) mixture of cholesteryl myrisate in which was dissolved 1.48% (by weight) of linearly dichroic β-carotene. The variation of circular dichroism with pitch exhibits anomalous behaviour, the sign of the dichroism being opposite below and above the nematic temperature. The peak value of the circular dichroism (per unit thickness) decreases as the sample thickness increases from 4 to 12.7μ. These features are in qualitative agreement with the predictions of the theory.