SURFACE-ENHANCED ORDERING AND LAYER-THINNING TRANSITIONS IN FREELY SUSPENDED SMECTIC-A FILMS

We propose a physical mechanism which leads to surface-enhanced smecti c-A ordering (SESO) at the free surface of a model liquid crystal. We also provide an explanation based on a density-functional theory, for recent experimental results for the melting behavior of freely suspend ed smectic (FSS) films. II is shown that stepwise layer-thinning trans itions do not usually occur during melting of FSS films, despite the p resence of SESO. We find that thinning transitions similar to those ob served experimentally occur under conditions such that the film interi or melts to a nematic rather than isotropic liquid phase.