A Molecular Dynamics Study on Nanobubble Coalescence Events in Heterogeneous Nucleation on a Hydrophilic Surface

Abstract

The bubble nucleation process has practical applications and has garnered a significant amount of attention. In the literature, researchers have commonly accepted that the incipient of the bubble nuclei is initiated by vapor trapping in cervices on the heated substrate. However, experimental observations have found that nucleation can occur with much lower superheat temperatures on ultrasmooth surfaces where vapor trapping is not applicable. To investigate the nucleation mechanism, molecular dynamics (MD) simulations were carried out to study nanobubble nucleation behavior on smooth and grooved hydrophilic substrates. The force field of argon atoms heated by solid substrates was described by using the Lennard-Jones (LJ) 12-6 potential field. The MD results revealed that the nanobubbles that emerged on the two- and three-groove surfaces could merge, forming a metastable nucleus via the coalescence event. The coalescence event lowered the required energy cost and accelerateed the nucleation process. Energy analyses also showed the bifurcation of the energy rise between the right and left regions of grooved surfaces. Furthermore, the mean first-passage time method was used to evaluate the corresponding critical nucleus volume and nucleation rate for all grooved substrates. The results suggest that nanobubble coalescence could be an alternative pathway in the nucleation process that could reduce the critical nucleus size and its associated energy cost. Show more