Validation of molecular dynamics simulation for a collapsing process of sonoluminescing gas bubbles

Abstract

Sonoluminescence is light emission associated with the catastrophic collapse of bubble oscillation under ultrasound. Molecular dynamics (MD) simulation of collapsing bubbles with micro- and nano-size equilibrium radii was performed and the results were compared with theoretical calculations. The molecules inside a collapsing gas bubble were modelled as hard spheres, and the instantaneous bubble radius and the bubble wall velocity used in the simulation were obtained from the Keller-Miksis equation with pressure data taken from MD simulation. With a suitable boundary condition at the bubble wall, the MD simulation results for the bubble wall velocity, the gas temperature and pressure around the collapse point for the sonoluminescing bubbles are in acceptable agreement with theoretical predictions. However, these theoretical predictions need validation because estimated thermal conductivity for the gas and liquid were used for the extreme condition achieved at the collapse point. This study also revealed that the collapsing process of a sonoluminescing gas bubble proceeds almost adiabatically.