Phase behavior and free interfaces of a lattice-gas nematic-liquid-crystal model

The phase behavior of a mesogenic lattice-gas model consisting of molecules located at the sites of a three-dimensional cubic lattice has been studied using grand canonical Monte Carlo simulations. When two neighboring sites are occupied, the molecules interact via a potential composed of an isotropic lattice-gas (LG) term and an anisotropic Humphries-Luckhurst-Romano (HLR) term [Mol. Phys. 42, 1205 (1981)]. The LGHLR model is shown to exhibit either nematic-isotropic, nematic-vapor (NV), and isotropic-vapor (IV) coexistence or just nematic-isotropic fluid coexistence, depending on the strength of the isotropic term. The liquid-vapor (i.e., NV and IV) interfaces were studied using canonical Monte Carlo simulations. By controlling the strength of the term that governs the anisotropy in the attractive forces, either planar or homeotropic anchoring is observed at the NV interface. The temperature dependencies of the density and order parameter profiles across the interfaces are determined for these two anchoring geometries.