On the Landau Description of the Reentrant Behavior in Liquid Crystals

Abstract

A Landau description of the reentrant nematic phase transition has been proposed by Cladis assuming a temperature dependent coupling between the nematic and smectic order parameters. In this paper it is shown that the reentrant phase transition can be driven by a temperature independent coupling between the nematic and smectic order parameters by removing some of the simplifications made by Cladis on the form of the expansion of the free energy excess in terms of the order parameters. A comparison of the results with experimental phase diagrams obtained for mixtures of some cyano-biphenyls, suggests that the coupling should, however, exhibit a weak temperature dependence. The possibility of double reentrancy is also discussed in this theoretical framework.