Thermal Behaviour and Electro-Optic Properties of a Nematic Exhibiting Cyclic Siloxane

Abstract

The thermal behaviour of a homologous series of cyclic siloxane liquid crystals with cyanobiphenyl terminal groups and alkoxy linkages is presented. One member of this series, with an n = 3 alkoxy spacer, exhibits a broad nematic phase and an above ambient glass transition. Excellent planar alignment was obtained in the nematic phase using low tilt rubbed polyimide, and uniform switching was seen on the application of a transverse electric field above threshold. Splay threshold voltages have been measured as a function of temperature and the splay elastic constant, K₁₁, calculated. For equivalent reduced temperatures, the splay threshold voltage and elastic constant for the cyclic - 3 OCB are similar to those for low molar mass 5CB. Electro-optic switching times and contrast ratios have been measured in a twisted nematic geometry. The effect may be stored below the glass transition.