Air bubble bursting phenomenon at the air-water interface monitored by the piezoelectric-acoustic method.

When an air bubble arrives at the free interface, the bubble's lamella drains and ruptures. The bubble collapses, and gas vapor is released. The ruptured lamella retreats, and a rim at the edge of the retreating lamella forms. The rim becomes unstable and breaks into fine droplets, leading to the formation of a mist. As the collapsing bubble gas's vapor is released, the collapsing bubble oscillates and a vertical liquid jet erupts; this jet then breaks into a droplet(s). Here, we present a novel approach for monitoring the air bubble bursting frequency at the air-water interface by the piezoelectric-pressure-acoustic technique. The piezoelectric-acoustic technique monitors the lamella's rupture time, the frequency of the oscillation of the collapsing air bubble, and the frequency of the oscillation at the free air/water interface. The aqueous lamella rupture thickness was probed by reflected light interferometry, and the air bubble burst at the air/water interface was monitored with the high-speed photo imaging technique. The data obtained by the three techniques provided essential information for the stages of the air bubble collapse dynamics at the free interface without the presence of a surfactant. The simple model proposed by Rayleigh, Minnaert, and Lighthill (RML) for the oscillation resonance of a single air bubble was applied to calculate the air bubble collapsing frequency. The floating air bubble bursting frequency with an equatorial radius of 0.33 ± 0.05 cm was well predicted using the air bubble resonance frequency model, and was estimated as 1.0 ± 0.3 kHz. The velocity of the ruptured aqueous lamella covering the air bubble was estimated as 1 m/s. This research presents a comprehensive understanding of the phenomenon of the bare air bubble collapse at the free interface.