Velocity and size quantification of drops in single and collective bursting bubbles experiments

Mechanisms of droplet production from bursting bubbles have been extensively studied for single bubbles, but remain sparsely investigated in more complex collective settings. We discuss jet and film drop velocity-size relationships from physics-based mechanisms, as a potential means to further differentiate between various mechanisms and correctly determine the drops origin. In a collective bubbling experiment, quasi-monodisperse subsurface bubbles rise up to the surface where, depending on the surfactant concentration, they can either merge or assemble in rafts of monodisperse bubbles. Drop trajectories are recorded, analyzed and shown to exhibit uniquely distinctive features for the different production mechanisms: centrifuge film drops are ejected sideways, jet drops are ejected vertically. Different single-burst scalings are finally compared to the experimental size-velocity relationships, and reveal that drops coming from collective bubble bursting appear slower and more scattered than when coming from single bursting bubbles.