Temperature compensated liquid crystal devices

Claim 1

A phase change liquid crystal device comprising two spaced slides at least one of which is transparent, electrode structures on the facing surfaces of the slides, means for spacing the slides apart, and containing a thin layer of a cholesteric liquid crystal material between the slides, the cholesteric liquid crystal material being a mixture of at least one liquid crystal material having a smectic and a nematic phase with at least one liquid crystal material having a cholesteric phase, the complete mixture having a positive dielectric anistropy and having the following phases with increasing temperature, crystalline--smectic--chloesteric--isotropic, the smectic to cholesteric transition occurring below the operating temperature of the device at a value selected from within the temperature range 10° to 60° C. whereby changes in k 22 (twist elastic constant)/ε a (dielectric constant) with temperature are at least partly compensated for by changes in cholesteric pitch P with temperature to stabilize the device threshhold voltage V th over a range of temperatures above the smectic to cholesteric transition temperature.