Dielectric studies of ferroelectric liquid crystals

Abstract

The dielectric properties of some ferroelectric alpha-chloroester thiobenzoate liquid crystal materials have been studied using a Du Pont 2970 dielectric analyzer (DETA) in the 0.01 Hz-100 kHz range. These materials exhibit smectic A and chiral smectic C mesophases, as well as additional mesophases in some cases. Transitions involving the chiral smectic C phase are of most interest because this phase has ferroelectric properties. The effect on these transitions of fluorine addition to the alkoxy tail was investigated. The Goldstone mode and soft mode are seen in the frequency dispersion curves of the dielectric loss factor. Very low heating rates of 0.01°C min-1 and small step-wise increments are possible, providing measurements at small temperature increments which permit close observation of the transition regions. DSC measurements and optical microscopy observations were also performed and the three techniques were found to be complementary. © 1991.