Dynamics of an oil jet produced by an oil-coated bubble bursting at a free surface*

Bubble bursting at a free surface is widely present in nature and industrial processes, and the resulting bubble bursting aerosols play an important role in mass transfer across the interface. Here, we experimentally investigate the jet dynamics from an oil-coated bubble bursting at a free surface. Such a configuration of a compound multiphase bubble encompasses a variety of fundamental problems and practical applications due to the heterogeneous nature of the fluid system. Examples include bubbles from subsea oil seeps and oily bubbles for froth flotation. However, the bursting dynamics of a compound bubble have not been well understood. Unexpectedly, we show that the jet mainly consists of oil, and the jet formation is affected by the oil properties and coating thickness. We further observe the cavity collapse and the oil motion during bursting with high speed imaging, to rationalize the effect of oil coating on the capillary wave focusing responsible for the jet formation. Finally, scaling laws are proposed to predict the jet tip radius and velocity. Our results not only advance the fundamental understanding of bubble bursting, but also may shed light on organic transport across the ocean-atmosphere interface by bubble bursting.