Basic Studies of Liquid Crystals as Related to Electro-Optical and Other Devices.
Final technical rept. 1 Jun 67-30 May 70
WESTINGHOUSE ELECTRIC CORP PITTSBURGH PA RESEARCH AND DEVELOPMENT CENTER
Pagination or Media Count:
The usefulness of optical devices, whose sensors consist of cholesteric liquid crystal combinations, is directly dependent upon the reproducibility of their color responses to changes in temperature and to electric fields. Many of the processes by which cholesteric liquid crystals lose their valuable optical properties were identified and steps taken to diminish or eliminate their effects. Oleyl cholesteryl carbonate, one of the essential components of field- and heat-sensitive liquid crystal mixtures, was found to decompose spontaneously to give CO and CO2 at a relatively small rate, which may still be too large in the case of applications involving sealed, evacuated systems. The thermal hysteresis observed in high temperature-sensitive liquid crystals was mainly dependent upon the material composition of the system and on the operating range. On shearing, cholesteric liquid crystal layers lost color intensity, but the wavelength of their maximum reflectance did not change appreciably. The rate of intensity recovery after cessation of shearing was linear with the logarithm of time. The main degradative process is brought about by the combined and cumulative influences of ultraviolet light, oxygen and air-borne particulates as a result, the color-bearing cholesteric structure is changed into a non-colored texture and the color responses are lost. This drawback was remedied by incorporating ultraviolet energy absorbers and polymeric protectants into the liquid crystal combinations. With these modified systems the useful life of cholesteric liquid crystal sensing systems was prolonged by several months. Author
- Physical Chemistry