Quantitative Thermodynamic Analyses of Nucleation, Evolution, and Stabilization of Surface Nanobubbles

The abnormal stability of nanobubbles has drawn significant interest from interfacial scientists and engineers. While thermodynamics is believed to dominate nanobubble dynamics, the precise mechanism by which nanobubble evolution is driven by thermodynamics remains unclear. It is essential to understand how nanobubble nucleation and growth, nanoscale contact line movement, and gas diffusion across the liquid-bubble interface are simultaneously driven by the change in free energy, leading to ultimate thermodynamic equilibrium of surface nanobubble systems. In this Letter, we propose a quantitative theoretical model to elucidate the thermodynamic dominance behind the dynamics and stability of the fluid system with surface nanobubbles. The present model demonstrates that thermodynamic nonequilibrium drives the gas diffusion and the contact line motion of surface nanobubbles. Overcoming the nucleation energy barrier is crucial for bubble nucleation and growth. Surface nanobubbles evolve toward the reduction of the system's free energy and stabilize at the state with minimum free energy. The thermodynamic equilibrium is accompanied by the mechanical equilibrium at the contact line and the gas diffusion equilibrium at the liquid-bubble interface, and the theoretical results are in excellent agreement with the nanobubble morphology observed in experiments.