Encapsulation by crossing of a liquid-liquid interface by a droplet at high inertia

Crossing of a liquid-liquid interface by particles has been essentially limited to solid particles so far. Here, we present an experimental investigation on the encapsulation of a droplet by crossing a liquid-liquid interface under centrifugal force using high-speed imaging. The aqueous droplets are injected into an oil phase through a capillary tube. The applied centrifugal force then drives the droplets towards the interface. Under adequate conditions, the droplets cross the interface, subsequently entraining a volume of the oil phase (liquid column) along with them, which ultimately pinches off leading to the coating of the droplet. We performed experiments for a wide range of process parameters and physical properties of the liquids, and obtained a "regime map" for the crossing conditions by plotting the density contrast ratio against the interfacial Bond number. We quantified the velocity and shape of the droplet as well as the coating volume, length and width of the entrained column as a function of relevant dimensionless numbers (We, Oh, Bo). In addition, we discuss the comparison with our recent numerical study as well as with previous studies on solid particles along with the role of surfactants.