Abyss Aerosols: Drop Production from Underwater Bubble Collisions

Over the past century, drops production mechanisms from bubble bursting have been extensively studied. They include the centrifugal fragmentation of liquid ligaments from the bubble cap during film rupture, the flapping of the cap film, and the disintegration of Worthington jets after cavity collapse. We show here that a dominant fraction of previously identified as "surface bubble bursting" submicron drops are, in fact, generated underwater, in the abyss, inside the bubbles themselves before they have reached the surface. Several experimental evidences demonstrate that these drops originate from the flapping instability of the film squeezed between underwater colliding bubbles. This finding, emphasizing the eminent role of bubble-bubble collisions, alters fundamentally our understanding of fine aerosol production and opens a novel perspective for transfers across water-air interfaces.