Influence of film thickness on the stability of free-standing Lennard-Jones fluid films.

Molecular dynamics simulations of thin free-standing Lennard-Jones fluid films were carried out with a view of establishing the thickness range over which such films are thermodynamically stable. Thermophysical and interfacial properties were studied as a function of film thickness, and we found that free-standing films at 116 K are no longer stable below a critical film thickness of about 3.3 nm in laboratory units appropriate for methane. In particular, films having a smaller thickness than this critical value collapsed to form spherical droplets. Although the size of our simulated system affects the thickness of the layers and the corresponding thickness of the interface and the densities of coexisting phases, the estimated surface tension was found to be remarkably insensitive to finite size effects. We also found that the standard deviation of the surface tension diminished with an increasing size of the simulation cell in the interfacial plane. However, these finite size effects do not alter the order of magnitude of the predicted critical film thickness and our qualitative conclusion that the surface tension is relatively insensitive to film thickness in these model thin films.