Molecular dynamics simulation of interfacial tension of ultra-thin liquid films on a solid surface

The effect of wall proximity on the interfacial tension of ultra-thin liquid films of Lennard-Jones (12,6) fluid has been studied using Molecular Dynamics Simulation. The wall's presence can potentially affect drop-wise condensation and other phase change phenomena such as boiling. Initially the LennardJones atoms are placed near a solid wall with FCC lattice structure in a doubly periodic box. Once equilibrated at a desired temperature, a thin liquid film forms on the solid wall. The surface tension of the liquid-vapor interface is computed statistically. When the film is thick (> 40 Å), surface tension at the liquid-vapor interface is found to be unaffected by the presence of the solid wall and matches bulk values reported for Argon. However for thinner films (< 15 Å), surface tension of the liquid-vapor interface deviates from the macroscopic value. This has been investigated for various temperatures ranging from the triple point to the critical point. As the film thins further (1-2 molecules thickness), the liquid-vapor interface resembles a solid-vapor interface. Surface tension of this solid-vapor interface is evaluated for a solid wall modeled both by an equivalent interacted potential and discrete atoms. The two cases are found to yield different results. The Equivalent potential for the wall gives lower surface tension and liquid density near the solid wall compared to the discrete atoms case.