Electro-optical and dielectric relaxation studies of an antiferroelectric liquid-crystal mixture (W-132A)

Abstract

Electro-optical properties and dielectric relaxation phenomenon have been investigated for antiferroelectric liquid-crystal mixture W-132A exhibiting SmA*, SmC*, and wide temperature range (∼0–48°C) induced SmCA* phases. Spontaneous polarization, tilt angle, response time, viscosity, relaxation frequency, dielectric strength, and distribution parameter have been determined as a function of temperature. Switching process has been studied in the antiferroelectric SmCA* phase with the help of transmission intensity-voltage characteristics. Impedance spectroscopy of the material under the planar anchoring conditioning of the sample has been carried out in the frequency range of 1Hz–10MHz. Usual soft-mode dielectric relaxation in the SmA* phase and Goldstone mode in the SmC* phase have been observed. A tendency of the soft mode to penetrate into the SmC* phase and that of the Goldstone mode into the SmCA* phase have been observed. The dielectric spectrum of the SmCA* phase exhibits two absorption peaks, namely, PL and PH modes which are separated by about two decades of frequency. PL is related to in-phase azimuthal angle fluctuation of the molecules in antitilt pairs, whereas PH is due to the antiphase fluctuation of the molecules in antitilt pairs.