Criteria for Antibubble Formation*

Antibubbles are fluid entities with the inverse phase of regular bubbles, i.e., liquid drops separated from the bulk liquid by a thin film of air. While relatively unfamiliar due to their ephemeral nature, antibubbles may arise when we wash dishes or pour beer into a glass. The form and stability of antibubbles, have previously been characterized using high-speed imaging techniques. In particular, the gravitational drainage of the bounding air gap and its effect on the lifetime of antibubbles have been widely discussed. The formation of antibubbles has received relatively little attention. We report here the results of an experimental study of antibubble formation. In the experiment, surfactant-added water droplets and jets impinge on the surface of the same liquid reservoir in order to create antibubbles. Criteria for antibubble formation are expressed in terms of two dimensionless groups, the Weber number and the relative magnitudes of the timescale of viscous drainage of air and the characteristic break-up time of the Plateau-Rayleigh instability.