DIELECTRIC AND ELECTROOPTICAL STUDIES OF A FERROELECTRIC COPOLYSILOXANE

This paper reports an extensive study of the static (spontaneous polarization, Ps, tilt angle θ, and pitch) and dynamic properties of a ferroelectric liquid-crystalline polymer. It is shown that a ferroelectric liquid-crystalline polymer (diluted polysiloxane) exhibits physical behavior similar to that of a low-molar-mass liquid crystal in terms of contrast ratio, pitch of the helix, and relationship between Ps and θ. The degenerated collective modes for the director rotation are shown to split into two modes at the Sm-A-Sm-C* phase transition temperature using dielectric spectroscopy. Both frequency and the inverse dielectric strength show critical slowing down behavior in the vicinity of the Sm-A-Sm-C* phase transition temperature. The dynamical behavior and the relative dependence of the dielectric strength on temperature for the soft mode in Sm-C* and Sm-A phase is consistent with the influence of a significant biquadratic coupling compared to its linear coupling between Ps and θ. The material parameters of the generalized Landau model for the diluted polysiloxane liquid-crystalline polymer have been found by fitting the experimental data to the mean-field theory. © 1994 The American Physical Society.