Specific optical properties of blends of cholesteric copolymers

Abstract

The phase behaviour of cholesterol containing liquid crystalline (LC) copolymers of different compositions (copolymers A and B), and the phase behaviour and optical properties of their blends have been investigated. The phase diagram of the mixture consisting of two fractions A and B with low molecular masses (MW<104) corresponds to complete solubility of the components over the whole concentration range. The transmittance spectrum of all blends has one minimum, which lies between two peaks corresponding to the wave lengths of the initial samples A and B. In the case of the cholesteric copolymers with molecular masses above 104, the corresponding phase diagram exhibits a lower critical solution temperature (Tcrit). Below Tcrit only one peak of the selective reflection of light is observed (SRL). However, above Tcrit two separate bands of SRL, corresponding to the reflection bands for the individual initial copolymers A and B are observed. The process of appearance of the single or double bands is reversible and by varying the temperature one can obtain films with bimodal or unimodal curves of SRL.