A molecular dynamics study of the atomic-level surface structural phase diagram for the existence form of nanobubbles and its influence in a dynamic system

Abstract

The nucleation of nanobubbles was studied through molecular dynamics (MD) simulations. The wettability and surface atomic-level structural features of the substrate were found to play a role in a ternary (solid, liquid, and gas) system that was composed of only simple Lennard-Jones fluids. The simulation first revealed that surface nanobubbles form only on a hydrophobic substrate, while for a hydrophilic substrate, bulk nanobubbles are formed in the liquid. Second, the existence form of nanobubbles and some behavioral characteristics strongly depend on the surface structural features. Specifically, we deduced the phase diagram of the nanobubbles with respect to the critical structural parameters and then defined a critical region for the formation of surface nanobubbles: cap-shaped surface nanobubbles can stably form above the upper critical line but not below the lower critical line; the contact angle decreases as the parameter value increases. Finally, the existence of nanobubbles was found to affect the dynamic properties of the system.