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.