Bistable switching and electroclinic effect of a low pitch and large spontaneous polarization ferroelectric liquid crystal mixture

Abstract

Switching time (ts, spontaneous polarization (Ps) and torsional bulk viscosity (yt) in the SmC* phase of a low pitch planar oriented ferroelectric liquid crystal mixture FLC#252 of thickness 15 μm have been measured in the temperature range of 25 to 52°C by the polarization reversal method. Optical tilt angle (θ) in the SmC phase and induced tilt angle (θind) in the SmA* phase produced by the electroclinic effect have been determined. Ps has been fitted on Ps = 27.32(Tc-T)044nC/cm2 below the Curie temperature Tc = 51.4°C. Ps is screened by the space charge from 25 to 35°C. ts lies in the range of 36 to 2 ms and varies inversely with E above a critical field Ec. The ratio Ps/sin2θ (= 512 nC/cm2) and the critical field Ec(= 1.20 kV/cm) are almost temperature independent from 25 to 44°C. yt, obeys the Arrhenius relation from 25 to 44°C with an activation energy of 0.36 eV. At room temperature yt is about 50 times larger than the phason rotational viscosity yφ. The flexoelectric coupling constant C and thermodynamic Landau parameter α are determined to be C = 0.33 × 108 V/m-rad and α = 0.23 × 105 N/m2-rad2-°C.