Properties of higher-ordered ferroelectric liquid crystal phases of a homologous series

Abstract

Four members of a homologous series of diarylethane α-chloroester ferroelectric liquid crystals [1] have been synthesized and characterized by polarizing optical microscopy and DSC measurements. Two of the compounds exhibit a twist grain boundary structure (TGB A* phase) or twisted smectic A* phase, shortly before reaching the smectic to cholesteric phase transition. The temperature dependence of the optical tilt angle θ, the spontaneous polarization Ps and the effective rotational viscosity γφ were investigated for the ferroelectric S*C, S*I and S*F phases. It was found that especially the spontaneous polarization and the rotational viscosity increased with decreasing length of the alkyl chain for all three ferroelectric phases. At the phase transition from S*C to S*I, all material parameters determined showed a discontinuous change, giving evidence for a first order transition. At the transition from the S*I to the S*F phase, the material parameters show only small, rather continuous changes.