Optical thermal and spectral studies of hydrogen bonded liquid crystals and thier binaries

Abstract

The discovery of the first Liquid Crystal LC in 1888 is attributed to Friedrich Reinitzer and thereafter wide research on LC is initiated by Scientists all over the globe Thermotropic liquid crystals are one in which temperature is varied to obtain phase polymorphism Yet another fascinating field of LC is hydrogen bonded liquid crystals HBLC This type of LC is first proposed by Paleos and latter extensive work is performed by Kato and his research group The complementary hydrogen bonds are formed between proton donor group and electron acceptor molecules Various shapes of HBLC are reported viz linear banana bent T shaped W shaped Y shaped Zigzag and U shaped These HBLC are unique with respect to their properties exhibited and further these physical properties can be co related to their molecular structure Thousands of HBLC are reported in literature with a variety of properties HBLC exhibits all conventional phases exhibited by calamatic rod like molecules in addition a few new smectic orderings like smectic X and smectic R are also noticed An interesting observation in HBLC is the parachromatism where the colour of the texture alters while the texture remains the same To enhance the desired properties in HBLC formation of binary mixtures is one fare choice By adding two HBLC complexes the desired properties like phase thermal width or altering the transition temperatures or phase polymorphism can be achieved A variety of properties like optical shuttering light modulation and light filtering can be commercially exploited The selection of the chemical ingredients is done in such a way that novel mesogenic liquid crystal homologous series are obtained newline