Mechanical Measurements of the Melting Transition in Thin Liquid-Crystal Films

Abstract

Shear mechanical properties of the liquid crystal 4-$n$-pentylbenzenethio-4′-$n$-tetradecyloxybenzoate ($\overline{14}\mathrm{S}5$) have been studied in films as thin as two molecular layers. Crystalline two-layer films were found to melt directly into a liquid phase by a large first-order transition. Crystalline films of three or more layers melted in two stages both by first-order transitions. Mechanical properties of the intermediate phase indicated crystalline surface layers with an anomalously soft response for a three-layer film.