Wetting-dewetting transition and conformal to non-conformal interfacial roughness transition in ultra-thin liquid crystal films on solid substrates

High-resolution X-ray reflectivity has been employed to study the structure, wetting properties, and interfacial roughness of ultra-thin liquid crystal films. The films were prepared at the air-water interface and transferred on to glass substrates by a modified horizontal deposition technique. A 3-layer film was found to partially-wet the substrate in the nematic and isotropic phases and dewet upon cooling to the crystalline phase. The surface roughnesses at the air-film and the film-glass interfaces exhibited a gradual reversible but hysteretic conformal (strongly correlated) to non-conformal transition between the isotropic and smectic-A phases.