X-ray reflectivity study of smectic wetting and prewetting at the free surface of isotropic liquid crystals - art. no. 041704

We study the structures of free-surface-wetting layers above the isotropic to smectic-ii transition of three liquid-crystal compounds that show differ ent kinds of growth of the wetting film as the bulk transition is approache d: layer-by-layer, continuous, and continuous with prewetting. The smectic- A surface phase of the layer-by-layer compound consists of well-defined lay ers and possesses a sharp boundary to the isotropic bulk phase, whereas in the two continuous compounds sinusoidal density oscillations with a continu ously decaying amplitude are found. In the continuous case with prewetting, the wetting film below the prewetting transition does not show an essentia l difference to the continuous case without prewetting.