Strong shear flows release gaseous nuclei from surface micro- and nanobubbles

The unexpectedly low cavitation inception threshold of water is widely attributed to the presence of cavitation nuclei either in the bulk water or attached to immersed surfaces. Being compressible, such objects are expected to respond to modest tensile stresses. Surprisingly, a large corpus of experiments shows that micro- and nanobubbles attached to planar smooth surfaces are unresponsive to tensile stresses, seemingly ruling out their ability to serve as cavitation nuclei. Here, using optical microscopy we show that, although these surface micro- and nanobubbles are not directly responsive to tensile stresses induced by a nearby cavitation bubble, strong short-lived shear flows induced by cavitation jetting cause tethers to extend from the surface micro- and nanobubbles and lead to the pinch-off of daughter bubbles. Our results show a unique and previously unanticipated mechanism for the generation of cavitation nuclei.