Molecular dynamics studies of bubble nucleation on a grooved substrate.

• Different bubble nucleation phenomena happen on the grooved substrates with different wettability. • A "PK" norm is developed to illustrate bubble nucleation mechanism. • The CNT about the liquid in the groove obtaining more thermal energy to achieve nucleating is verified by the "PK" norm. • The advantage of strongly hydrophilic groove on bubble nucleation is revealed by the theoretical approach and "PK" norm. • The CNT about some residual gases in the groove becoming an initial bubble nucleus is explained by "PK" norm. • The mechanism for growth of initial bubble nucleus from the strongly hydrophobic groove is explained by "PK" norm. • The "PK" norm is available to explain the existence of solid-like liquid atoms on the hydrophilic substrate surface. • The "PK" is a good tool to determine the incipient nucleation time. The classical heterogeneous nucleation theory explains that the groove in the substrate is a desirable place to breed a bubble nucleus. However, the existing research method cannot reproduce the nucleation process. Therefore, in the present study, the molecular dynamics simulation method is conducted to investigate the bubble nucleation on grooved substrates with different wettability. The simple L-J liquid argon is heated by the platinum grooved substrate, whose temperature is controlled by Langevin thermostat. Results show that the groove has significant impacts on bubble nucleation from two aspects: improve thermal energy transfer efficiency and support an initial bubble nucleus. For the substrate with a hydrophilic groove, a visible bubble nucleus generates on the groove region from nothing because of liquid in there obtaining more thermal energy than that on the smooth region within the same time. Moreover, the nucleation rate is improved with the increase of groove hydrophilicity. On the other hand, for the substrate with a hydrophobic groove, some residual gases form an initial bubble nucleus at the initial moment of the nonequilibrium simulation stage, and it takes some time to grow up. Furthermore, a method based on the competition between atomic potential energy and atomic kinetic energy is used to explain the formation of the bubble nucleus on the different wetting substrates. The present simulation study of bubble nucleation on the grooved substrate is another support for the classical heterogeneous nucleation theory. [ABSTRACT FROM AUTHOR]