High pressure studies on ferroelectric liquid crystals

Abstract

We present here an overview of our high pressure investigations on ferroelectric liquid crystals. We begin with a brief description of the optical and electrical high pressure set up, followed by data highlighting the influence of pressure on a variety of properties. The results can be summarized as follows. At a constant relative temperature (with respect to the A–C* phase boundary) the spontaneous polarisation (P_s) decreases linearly with increasing pressure, whereas the coercive field E_c' the critical field E_u for unwinding the helix and the rotational viscosity γΦ associated with ferroelectric switching increase linearly with pressure. The temperature and frequency dependence of the transverse dielectric constant show more dramatic changes. The dominant effect on the dielectric constant appears to be due to the slowing down of the director relaxation modes, viz., the Goldstone mode and the soft mode with pressure. The ferroelectric switching time estimated from the simple relation τ = γ /P_s E shows a linear increase with pressure. Experiments are in progress to measure the pressure dependence of the pitch.