Molecular mechanism for cavitation in water under tension

TL;DR

This study uses computer simulations and theoretical models to elucidate the molecular mechanisms of cavitation in water under tension, highlighting the roles of bubble shape, surface tension, and viscous forces in bubble growth and nucleation rates.

Contribution

It demonstrates that classical nucleation theory with curvature-dependent surface tension accurately predicts cavitation free energy and rates, aligning well with experimental data and providing new insights into nanoscale bubble dynamics.

Findings

Bubble shape evolves from irregular to spherical during growth.

Classical nucleation theory with curvature-dependent surface tension matches simulation data.

Viscous forces govern nanoscale bubble growth, enabling accurate cavitation rate predictions.

Abstract

Despite its relevance in biology and engineering, the molecular mechanism driving cavitation in water remains unknown. Using computer simulations, we investigate the structure and dynamics of vapor bubbles emerging from metastable water at negative pressures. We find that in the early stages of cavitation, bubbles are irregularly shaped and become more spherical as they grow. Nevertheless, the free energy of bubble formation can be perfectly reproduced in the framework of classical nucleation theory (CNT) if the curvature dependence of the surface tension is taken into account. Comparison of the observed bubble dynamics to the predictions of the macroscopic Rayleigh--Plesset (RP) equation, augmented with thermal fluctuations, demonstrates that the growth of nanoscale bubbles is governed by viscous forces. Combining the dynamical prefactor determined from the RP equation with the free energy of CNT yields an analytical expression for the cavitation rate that reproduces the simulation results very well over a wide range of pressures. Furthermore, our theoretical predictions are in excellent agreement with cavitation rates obtained from inclusion experiments. This suggests that homogeneous nucleation is observed in inclusions, whereas only heterogeneous nucleation on impurities or defects occurs in other experiments.