The Interfacial Properties and Thermodynamic/Kinetic Stabilization Mechanisms of Bulk Nanobubbles: A Molecular Dynamics Simulation Study
Xuesong Zhang, Zhenzhong Fan, Yuanfeng Fu, Li Cai, Jingang Liu
Abstract
Bulk nanobubbles can remain stable in solution for hours or days, but the stabilization mechanism of bubbles remains highly controversial, lacking systematic research and theoretical explanations. This study employed molecular dynamics simulation, using an all-atom model to construct nitrogen and oxygen nanobubbles of different sizes, and conducted a systematic analysis of nanobubble stabilization mechanisms from multiple dimensions, including thermodynamics, mechanical mechanics, energetics, and diffusion dynamics, while verifying the applicability of certain theories and equations. The research results indicate that the gas density inside nanobubbles is significantly higher than that under standard temperature and pressure conditions by more than 2 orders of magnitude. The bubble surface forms a gas-liquid interface layer and hydration layer, which decreases with increasing bubble size. The hydrogen bond structure density on the bubble surface is smaller than that in liquid water, and the charge distribution exhibits a typical "positive inside, negative outside" double-layer structural characteristic. There is a significant pressure difference inside and outside the bubble, a phenomenon that conforms to the Young-Laplace equation. The dynamical simulation results are consistent with the diffusion coefficients calculated by the Einstein-Stokes equation, and the gas diffusion capacity decreases with increasing bubble size. The gas solubility inside the bubble is far higher than the standard state saturation solubility calculated by Henry's law. The results are consistent with the Epstein-Plesset theoretical trend of nanobubble lifetime. This study enhances the microscopic-level understanding of nanobubble stabilization mechanisms, providing a critical theoretical basis and practical guidance for their potential applications in cavitation and mass transfer within water treatment.