Effect of Different Polar Groups on the Mesomorphic and Physical Properties of Synthesized Schiff Base Liquid Crystalline Compounds

Abstract

Five compounds of calamitic Schiff base with liquid crystalline behavior were synthesized and characterized. The terminal of compounds were substituted with different types of polar groups are        - OCH₃, -COCH₃, - Br, and -COOC₂H_5, -CF₃. The chemical structures of all compounds were characterized by FTIR spectroscopy while the phase transitions and optical textures of the samples were observed by polarized optical microscope. Furthermore, the transition temperatures of the compounds and their liquid crystalline temperature range were determined by using differential scanning coulometer. All compounds showed a higher tendency to exhibit an antiotropic nematic mesophases with different transition temperature range. Moreover, the dielectric and electrical conductivity were investigated. Using different polar groups in the synthesized liquid crystalline compounds is accompanied by significant changes in mesophase thermal stabilities as well as physical properties and all samples are with positive dielectric anisotropy.