Formulation of a room temperature ferroelectric liquid crystal mixture with sub-millisecond switching time

Abstract

Ferroelectric liquid crystal (FLC) based display devices show faster response compared to nematic LC based devices. Since pure FLC compounds are high temperature LCs and do not possess optimum parameters necessary for display devices, a room temperature FLC mixture has been formulated, first time by any Indian group. The mixture is prepared by doping an appropriate chiral compound in a four-component LC based achiral host mixture. Resulting mixture was characterized using optical polarizing microscopy, frequency domain dielectric spectroscopy and electro-optic methods. It shows very wide range ferroelectric SmC* phase followed by paraelectric SmA* phase (Cr< 19°CSmC*89°C SmA* 108°C I) which would facilitate attaining book shelf geometry alignment in display devices. Dielectric spectroscopy study reveals Goldstone (in kHz region) and soft mode (in hundred kHz region) relaxations in SmC* and SmA* phases respectively. The mixture possesses moderate tilt angle (34.5⁰ - 13⁰), low viscosity (0.9 – 0.05 N.s.m−2) and moderately high spontaneous polarization (112 – 36 nC.cm−2) which decrease with temperature. These result in very fast switching, slowest response time being 475 µs at ambient temperature.