Dynamics of the Director Reorientation and Light Modulation in Helix-Free Ferroelectric Liquid Crystals

Abstract

The dynamics of the director reorientation in new helix-free ferroelectric liquid crystals (FLC) is considered. These materials are specially designed helix-free FLCs with a rather low value of the spontaneous polarization (less than 50 nC/cm2) and high viscosity (from 0.3 to 1.0 Poise), which are characterized by a spatial periodic deformation of smectic layers in the absence of an electric field. FLC director reorientation is due to the motion of solitons – spatially localized waves of a stationary profile that arise in an alternating electric field upon transition to the Maxwellian mechanism of energy dissipation. A theoretical model is proposed for describing the spatial-periodic deformation of FLC and reorientation of its director. The frequency and field experimental dependences of FLC electro-optical response time are presented for the modulation of the light transmission with fastest response among all LC materials. The novel helix-free FLC are able to efficiently modulate the visible and near IR radiation at frequencies up to 7 kHz at the electric field strength of the order of 1-2 V/μm. The conditions for the continuous hysteresis-free electro-optical response were determined, and such a response was realized for the first time in the frequency range up to 6 kHz.