Ferroelectric Properties of Chiral Smectic Liquid Crystal

Abstract

The dielectric properties of L-p-alkoxybenzylidene p'-amino 2 methylbutyl cinnamate are studied. The dielectric constant depends strongly on the dc bias field E and shows hysteresis, in the chiral smectic-C phase but not in the smectic-A phase. The D–E characteristic under dc conditions evaluated from the εr–E characteristic, also shows hysteresis in the chiral smectic-C phase of compounds with long alkoxy chains (n≥6; n: carbon number of the alkoxy chain). The spontaneous polarization measured by this method is 0.0015 µC/cm2, which is close to the value measured by the Sawyer-Tower method (60 Hz). However, the hysteresis loop and the coercive field estimated by the dc method are smaller than in the Sawyer-Tower method, indicating that the mono-domain structure relaxes back to the original multi-domain structure in a much shorter time than in ordinary solid ferroelectrics. The dependence of the dielectric constant on the measuring frequency and the alkoxy chain length are also studied. The influence of the alkoxy chain length in hindering the free rotation of a molecule around its long axis is discussed.