Molecular Dynamics Study on the Stability of Nanobubbles: From Stretch to Compression

Abstract

This work systematically investigates the stable states of argon vapor nanobubbles emerging in bulk liquid under either stretch or compression using molecular dynamic simulation. Thermodynamic conditions including the average density of argon atoms in the system, scale of the simulation box, and temperature are changed in various simulation cases. A new approach that considers the curvature effect of the gas–liquid interface on surface tension was proposed to distinguish the phase boundary of the nanobubble, by which the stability of the nanobubble is analyzed. The stable states of nanobubbles are judged by time-averaging the system pressure at equilibrium: positive system pressure means that the nanobubble is compressed, while negative pressure means that the nanobubble is stretched. By decreasing the average argon density, increasing the system scale, or increasing the temperature, the stable state of argon vapor nanobubbles changes from stretch to compression. Under higher compression, the phase interfaces are vague and deformable and the nanobubble destabilization temperature is closer to the critical temperature. The Laplace pressure becomes lower, and the decrease in system pressure due to nanobubble destabilizing is less significant under compression than under stretch.