A Molecular Statistical Theory of Antiferroelectric SmecticALiquid Crystals

Abstract

Thermodynamic stability of antiferroelectric smectic A liquid crystals with polar molecular shapes is examined on the basis of a molecular theory. The polar smectic A molecules are modeled into a nail-like one composed of two cylindrical parts. The excluded-volume effect between molecules is taken into account within the second-virial approximation. The numerically evaluated pressure-temperature phase diagrams for such antiferroelectric smectic A systems imply that the increasing polarity of the molecular shape stabilizes the bilayer smectic structure rather than the monolayer smectic structure because of the lateral steric hindrance through the heads of the naillike molecules. It is shown that with increasing temperature under a constant pressure the polar smectic A system have two successive transitions according to the scheme: monolayer SA phase→bilayer SA phase→nematic phase.