High-Pressure Investigations of a Ferroelectric Liquid Crystal Exhibiting a Trend Reversal in the Thermal Variation of Polarization

Abstract

In contrast to the exhaustive measurements of various properties of ferroelectric liquid crystals at atmospheric pressure, only a few studies exist at high pressure. Here we report the isobaric thermal variation of spontaneous polarization (P(s)), coercive voltage (U(xc)), and rotational viscosity (γ(ϕ)) of a ferroelectric liquid crystal (10PPBN4) as a function of applied pressure. The material having a high value of P(s) exhibits a trend reversal: as the temperature is lowered below the transition from the smectic A to the smectic C* (ferroelectric) phase, P(s) increases to begin with but after reaching a maximum decreases with further decrease in temperature. Interestingly, the trend reversal feature becomes more dominant as the pressure is increased. Further, at a fixed reduced temperature with respect to the transition, all three parameters P(s), U(xc), and γ(ϕ) decrease with pressure. We show that the data can be well described by a model developed for materials exhibiting a sign reversal in P(s). The single characteristic parameter of the model, viz., the ratio of the inversion temperature (at which P(s) changes sign), to the transition temperature, is seen to increase with pressure, corroborating predominance of trend reversal at elevated pressures observed experimentally.

Pressure and temperature dependences of ferroelectricity in liquid crystals

“…From PVT and DTA data they observed that the temperature range of the Sm C phase diminishes with increasing pressure and above 350 MPa a new phase appears. As compared to achiral mesogens, however, only few measurements on FLCs under elevated pressure are available [2][3][4][5][6][7][8][9][10][11][12] which show that the properties of FLCs change significantly and a number of pressure driven new and interesting features are observed.…”