Dielectric properties of ferroelectric liquid crystals with lateral group in the core

Abstract

Two series of ferroelectric liquid crystalline materials, non-substituted and containing a methoxy lateral group at the aromatic ring of the molecular core have been investigated by dielectric relaxation spectroscopy in the range from 1 Hz to 1 MHz. All compounds exhibit chiral SmC* phase. A low temperature ferroelectric phase, consisting of the ordinary SmC* phase and a crystalline phase, was detected in three of the investigated compounds. The frequency dispersion reveals two modes (denoted as mode 1 and mode 2) detected in both ferroelectric phases. The analysis of the frequency dispersion of the complex permittivity provides relaxation frequency and dielectric strength of these modes. In the SmC* phase, high frequency mode 1 is the Goldstone mode. Low frequency mode 2 is attributed to a non-homogenous distribution of ionic space charge, which is localized near the surfaces. The values of P s in the low temperature ferroelectric phase are lower than in the ordinary SmC* phase for the methoxy substituted compounds but shows no anomaly for the non-substituted material.