Structures and electric field effects in ferro-, ferri- and antiferro-electric liquid crystal devices

This paper reviews several experimental studies of electric-field effects in liquid crystal devices containing ferroelectric, anliferroelectric and ferrielectric liquid crystals. Small-angle X-ray scattering has been employed to study both rapid, reversible layer flexing and irreversible, high-field deformations in surface stabilised ferroelectric devices. New antiferroelectric materials are also considered and the tilt angle and chevron angle adopted in devices are described. Generally, the chevron angle is found to compare well with the steric tilt angle (∼20°) and is considerably lower than the optical tilt angle (∼30°). Both conventional and resonant X-ray scattering experiments have been used to probe the layer and interlayer structure and field-induced deformations in antiferroelectric, ferrielectric and ferroelectric liquid crystal devices. It is found that the mechanism of the chevron to bookshelf transition is phase-dependant and is thresholdless in the ferroelectric phases of these materials. Further, resonant scattering reveals that the field-induced antiferroelectric or ferrielectric to ferroelectric transition can occur at field strengths that are similar to or higher than those required to deform the smectic layers.