An atomistic simulation study of the role of asperities and indentations on heterogeneous bubble nucleation

Heterogeneous bubble nucleation was studied on surfaces having nanometer scale asperities and indentations as well as different surface-fluid interaction energies. Nonequilibrium molecular dynamics simulations at constant normal stress and either temperature or heat flux were carried out for the Lennard-Jones fluid in contact with a Lennard-Jones solid. When surface defects were of the same size or smaller than the estimated critical nucleus (the smallest nucleus whose growth is energetically favored) size of 1000-2000 angstrom(3), there was no difference between the defected surfaces and atomically smooth surfaces. On the other hand, surfaces with significantly larger indentations had nucleation rates that were about two orders of magnitude higher than the systems with small defects. Moreover nucleation was localized in the large indentations. This localization was greatest under constant heat flux conditions and when the solid-fluid interactions were weak. The results suggest strategies for enhancing heterogeneous bubble nucleation rates as well as for controlling the location of nucleation events.