Capillary condensation and snap-off in nanoscale contacts

When a surface is placed in a vapor, several layers of molecules may adsorb depending on the intermolecular forces involved. As two such surfaces are brought together, a critical point is reached at which the gas condenses be tween the surfaces, forming a capillary across the gap. A cohesive force is associated with the condensed bridge. The reverse process wherein the capi llary bridge degenerates as the surfaces are moved apart is called snap-off . These processes play a profound role on scales from the nano to the macro . We have studied this phenomenon via isostrain grand canonical Monte Carlo statistical mechanical simulations for Lennard-Jones fluids. Specifically, we have examined capillary condensation and snap-off between nanocontacts, infinite rectilinear nanowires, and finite rectilinear nanoplatelets, wher e macroscale concepts and theories are just about impossible to apply. Thes e results are compared to condensation between infinite parallel plates. We discuss our results in terms of the Kelvin equation and van der Waals film -thickening model.