Biaxial dielectric properties of phenyl ester ferroelectric liquid crystal mixture

Dielectric and electro-optic properties of phenyl ester FLC mixture have been studied in detail. Dielectric relatation spectroscopy was used to study the molecular dynamics and dipolar ordering. In the SmA* phase, this is accompanied by a sharp increase in the dielectric strength Delta epsilon(s) on approaching T(c). At such high frequency (2 MHz) Delta epsilon is usually negative in the SmC* and SmA* phase. In the N* phase, at lower frequencies, Delta epsilon had a weakly positive value. In the SmC(*) phase, delta epsilon is positive and its maximum value is less than 0.1. The dielectric biaxiality is discussed as an order parameter of the tilted smectic phase. It is verified that if the tilt angle increases according to theta proportional to (T(C) - T)(beta), the biaxiality increases according to delta epsilon proportional to (T(C) - T)(2 beta). A critical exponent for theta and delta epsilon are 0.27 and 0.54, respectively. The rotational viscosity gamma(theta) for soft mode is of 10 Nsec/m(2) in the SmA* phase. The activation energy for the rotational dynamics of Goldstone mode is estimated to be 1.4 eV from an Arrhenius plot. Optical response time is of about 50 mu s at room temperature in SmC* phase, and is on the order of 10 mu s in the N* phase and almost independent of the applied field. (C) 2000 Kluwer Academic Publishers.