Mechanical stability of surface nanobubbles

Bubble cavitation is important in technologies such as non-invasive cancer treatment and diagnosis, surface cleaning, and waste-water treatment. The cavitation threshold is the critical external tensile pressure that induces unstable growth of the bubble. Surface nanobubbles have been previously shown experimentally to be stable down to -6MPa, in disagreement with the Blake threshold, which is the classical cavitation model that predicts bulk bubbles with radii ~100nm should be unstable below -0:6MPa. Here we use Molecular Dynamics (MD) to simulate quasi-2D and 3D nitrogen surface nanobubbles immersed in water, subject to a range of pressure drops until unstable growth is observed. We propose and assess new cavitation threshold models, derived from mechanical equilibrium analyses for both the quasi-2D and 3D cavitating bubbles. The discrepancies from the Blake threshold are attributed to the pinned contact line, within which the surface nanobubbles grow with constant lateral contact diameter, and consequently a reduced radius of curvature. We conclude with discussion of previous experimental results on the cavitation of relatively large surface nanobubbles.