Influence of Film Thickness on the Stability of Free-standing Lennard-Jones Fluid Films
Jack F. Douglas, Jose Rivera
We carried out molecular dynamics simulations on thin free-standing films of Lennard-Jones fluid with a view of establishing the range in which the films are thermodynamically stable. thermophysical and interfacial properties were studied as a function of the film thickness. We find that the films are no longer stable below a critical film thickness. Layers below this critical value collapse to form spherical droplets. In laboratory units, this scale corresponds to 3.32 nm for methane at 137.23K. This thickness scale is comparable to bridging layers of water in hydrophilized nanotubes. Although the size of our simulated system affects the thickness of the interface and the densities of coexisting phases, the surface tension remained remarkably insensitive to finite size effects, although, the standard deviation of the surface tension decreased to considerable low values as the size of the simulation cell grows in the surface directions. For layers free of the size effects the standard deviations will reach a value of 2.8 %. Size effects induces higher pressures at the interface in the normal and tangential directions, which ultimately produces narrower critical thicknesses when shorter simulation cells in the directions of the interfacial surface are used.