Melting of Variable-Thickness Liquid-Crystal Thin Films: A Synchrotron X-Ray Study

Abstract

The results of a synchrotron x-ray study of the crystalline-$B$ to smectic-$A$ melting transition in 4-$n$-pentylbenzenethio-4′-$n$-tetradecyloxybenzoate ($\overline{14}\mathrm{S}5$) are presented. Samples of two, three, five, and twelve molecular layers were investigated with the freestanding thin-film technique. A single, abrupt, hysteretic transition is observed in two-layer films with temperature-independent positional correlations above the transition. All thicker films melt by two first-order phase transitions; the character of the intermediate phase depends strongly on film thickness.