Liquid encapsulation by binary collisions of immiscible liquid drops

In this paper, we present binary collisions of immiscible liquid drops as a promising and reliable process for encapsulating liquids in shells of other, immiscible liquids. Our current experimental approach describes the collision outcome according to relevant parameters. Depending on the drop size and the relative velocity, the impact parameter and liquid viscosity, density and surface tension, we observe that either the full drop of encapsulating liquid spreads around the encapsulated one, or part of it separates, while the rest remains attached. We show that the viscosities of the two liquids do not have equal importance for the stability limit of the process, especially for head-on collisions. For separation after the collision, a new mechanism is identified which does not occur with miscible liquid drop collisions. For separated drops, the thickness of the remaining liquid shell was also investigated and turns out to be independent of both liquid viscosities and relative velocity. As a consequence, we can accurately adjust the thickness of the coating layer by simply tuning the impact parameter of the collision. An interpretation of this behavior based on a geometric argument is proposed.