Molecular dynamics study on effects of bubble-bubble interaction and thermal fluctuation on stability of nanobubbles in bulk water

Recently, existence of bulk nanobubbles (Bulk NBs) in water for a long time has been confirmed experimentally, but necessary conditions for their stable existence have not been well understood. Among the various studies on their stable existence, Hong et al. simulated Bulk NBs by applying the periodic boundary conditions (PBC) to one bubble in the computational domain using molecular dynamics (MD) method, and indicated that there is the maximum interbubble distance for the stable existence. Furthermore, the relation between the bubble radius and the maximum interbubble distance was proposed by a simple model. However, in their study, the effect of bubble radius changes due to thermal fluctuation was not considered. In this study, we studied the effect of bubble radius change by thermal fluctuation on the relation between bubble radius and interbubble distance in stable Bulk NBs. In addition, we investigated Bulk NBs in water using MD with partial elimination of PBC and evaluated lifetime of the bubbles. As a result, it was suggested that NBs are harder to exist in the system where the bubble radius is to be changed by the thermal fluctuation, compared to the study by Hong et al. Furthermore, MD simulation partially eliminating PBC showed that the larger bubble grows while the smaller one shrinks due to the effect of thermal fluctuation. Therefore, it was clear that an appropriate elimination of influence of PBC is necessary for a realistic explanation of existence of Bulk NBs in MD simulations.