Partial coalescence between a drop and a liquid-liquid interface

This Letter reports experimental results for partial coalescence when a drop merges with an interface. We find an intermediate range of drop sizes in which the merger is not complete but a daughter drop is left behind. This phenomenon is governed primarily by inertia and interfacial tension, and three regimes can be further delineated depending on the roles of viscosity and gravity. Scaling relationships are developed for the drop size ratio and the coalescence time. For drops that are too large or too small, partial coalescence is arrested by gravity or viscosity, respectively. (C) 2006 American Institute of Physics.