THEORY ON THE CONTRIBUTION OF HEAD-TAIL ASYMMETRY OF A MOLECULE TO THE PHASE-TRANSITIONS IN CHIRAL SMECTIC LIQUID-CRYSTALS

A chiral rod-like molecule has the head-tail asymmetry, so that the pair potential between such molecules in head-to-head configuration is naturally different from the potential of those in tail-to-tail or head-to-tail configuration. Taking the head-tail asymmetry into account, we propose a simple model of chiral smectics and calculate the free energy of possible phases in a mean field approximation. The results show that the head-tail asymmetry can contribute to stabilize certain type of antiferroelectric phase between the ferroelectric smectic-C* phase and the antiferroelectric smectic-C-A* phase.