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 Δεs on approaching Tc. At such high frequency (2 MHz) Δε is usually negative in the SmC* and SmA* phase. In the N* phase, at lower frequencies, Δε had a weakly positive value. In the SmC* phase, δε 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 θ ∝ (TC − T)β, the biaxiality increases according to δε ∝ (TC − T)2β. A critical exponent for θ and δε are 0.27 and 0.54, respectively. The rotational viscosity γθ for soft mode is of 10 Nsec/m2 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 μs at room temperature in SmC* phase, and is on the order of 10 μs in the N* phase and almost independent of the applied field.