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 P _s and the effective rotational viscosity γ_ø 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*₁ to the S*_F phase, the material parameters show only small, rather continuous changes.