Mixed liquid crystals: additive effect of terminal polar groups in Schiff bases

Abstract

Evidence on the additive effect of the terminal polar groups of linear organic compounds has been obtained. The extent of mixed mesomorphism in binary systems of Schiff bases and p-azoxyanisole is dependent largely on the polarisability of the terminal groups. The higher the polarisability of the terminal groups, the greater is the area of mixed mesomorphism in the phase diagrams. Even terminal groups which exhibit least polarisability give rise to mixed liquid-crystals but to a much less extent. The relative behaviour of Cl, Br, and I suggests however that other factors such as size of terminal substituents are also important. A quantitative evaluation of the additive effect has been made which would strengthen the quantitative view of the effect of structure on mixed liquid-crystal formation.