Surface-enhanced ordering and layer-thinning transitions in freely suspended smectic-A films

4 pages, 3 figures.-- PACS nrs.: 61.30.Cz, 64.70.Md, 68.45.Gd.We propose a physical mechanism which leads to surface-enhanced smectic-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 suspended smectic (FSS) films. It is shown that stepwise layer-thinning transitions do not usually occur during melting of FSS films, despite the presence of SESO. We find that thinning transitions similar to those observed experimentally occur under conditions such that the film interior melts to a nematic rather than isotropic liquid phase.This work was supported by the DGICyT of Spain (Grant No. PB94-0005-C02) and NSERC of Canada.Publicad