Tuesday, November 6, 2007 - 4:12 PM

Observation Of Surface Phase Transitions At The Solid - Liquid Crystal Interface Via Molecular Simulation

Erich A. Muller1, José M. Romero-Enrique2, and Luis F. Rull2. (1) Chemical Engineering, Imperial College London, London, SW7 2AZ, United Kingdom, (2) Departamento de Física Atómica, Molecular y Nuclear, Universidad de Sevilla, Sevilla, Spain

Molecular simulations which evidence the existence of surface phase transitions of a Gay-Berne liquid crystal model vapor placed in contact with an unstructured attractive wall are reported. Monte Carlo simulations are performed in the Grand-canonical ensemble on a wide pore at a range of temperatures corresponding to states below and above the bulk nematic-isotropic-vapor triple point. The analysis of the adsorption isotherms show evidences of a first-order prewetting transition. In addition, a surface nematization of the first fluid layer close to the substrate, i.e. a surface phase transition between a disordered film and a nematic-like film, is observed. The nature of the ordered film is studied and is shown to be analogous to a two-dimensional Gay Berne fluid. For the lowest temperatures both transitions occur simultaneously. However, as the temperature is increased, surface nematization transition is observed after prewetting. At the highest temperatures, prewetting is not observed, and surface nematization occurs for isotropic liquid bulk conditions.