Molecular dynamics simulation on bubble formation in a nanochannel

Molecular dynamics simulations are carried out to examine the bubble behavior confined in a nanochannel with particular emphasis on the nucleation phenomenon. Simple Lennard-Jones fluids are under consideration and nano-sized bubbles are observed under different conditions of solid-liquid interfacial wettability. It is found that the bubble nucleation behavior shows a marked dependence on the solid-liquid interfacial interaction. In particular, it is found that bubbles appear in the bulk liquid homogenously for a hydrophilic surface, but grow directly on a hydrophobic solid surface. Also, a bubble will not form on a non-wetting surface. A nanobubble exists stably under the equilibrium state and the number density distribution of the curved liquid-vapor interface is examined. It is also found that there are few vapor atoms in the nano-sized bubble and the internal vapor pressure of the nanobubble is much lower than that required from the Young-Laplace equation. The disagreement with the prediction of the Young-Laplace equation can be attributed to the fact that the liquid-vapor interface region plays an important role on the force balance at the curved liquid-vapor interface of a nanobubble. (c) 2006 Elsevier Ltd. All rights reserved.