Partial coalescence of a soap bubble with a soap film*

When a droplet is gently deposited on a liquid bath, it may coalesce only partially thereby releasing a daughter droplet of approximately half the size of the parent droplet. While the partial coalescence of droplets has been extensively studied, recent numerical simulations have suggested that partial coalescence should also be possible for soap bubbles. We present here the first experimental study of the partial coalescence of a soap bubble with a soap film. The coalescence process occurs over a timescale comparable to the inertial-capillary time, which is the time for the capillary waves generated during the process to span the bubble. A simple model that captures the time variation of the bubble's size during the air evacuation phase is presented. Through dynamic similarity, the process for bubbles is remarkably similar to that for droplets. In particular, daughter bubbles are observed to be approximately half the size of their parents and can exhibit a coalescence cascade, which arises as a succession of partial coalescence events. Future directions and ongoing work will be discussed.