Dielectric behavior at the smectic-C*-chiral-nematic phase transition of a ferroelectric liquid crystal.

Abstract

The dielectric relaxation processes of a ferroelectric liquid crystal material with a first order phase transition (chiral-nematic to smectic-${\mathit{C}}^{\mathrm{*}}$) have been investigated using thin, gold coated electrode cells in the frequency range of 10 Hz to 13 MHz. The results have been reported for planar and homeotropic aligned cells. The surfaces of the electrode cells were not given any surface treatment for alignment in order to minimize the surface anchoring effect on the dielectric processes. The orientation was done by a magnetic field. It has been observed that in planar alignment three dielectric collective processes, namely, the Goldstone mode, domain mode, and soft mode, connected to the director reorientation were detected. The soft mode process obeys the Curie-Weiss law at the temperature of the Sm-${\mathit{C}}^{\mathrm{*}}$ to ${\mathit{N}}^{\mathrm{*}}$ phase transition. In homeotropic alignment the molecular relaxation around the short axis of the molecule has been observed in the ${\mathit{N}}^{\mathrm{*}}$ phase. The results have been discussed in view of temperature dependences of the different dielectric processes in planar alignment with respect to the relaxation frequency and dielectric strength in the smectic-${\mathit{C}}^{\mathrm{*}}$ and chiral-nematic phases. For homeotropic alignment it is reported in the ${\mathit{N}}^{\mathrm{*}}$ phase only. \textcopyright{} 1996 The American Physical Society.