Experimental and analytical studies on colliding merging of two immiscible drops

Two types of merging between two immiscible drops have been found in their collisions. Depending on the interfacial tensions among the three media of different components, including air and immiscible liquids, at an equilibrium state with negligible impact energy, partial engulfing and complete engulfing between the drops can be identified. With sufficient inertia of relative motion between the drops, it would yield adhesive merging, whereby two drops adhere to each other, or encapsulation, whereby the softer drop totally encapsulates the harder one which has higher surface tension. Based on two dimensionless numbers, a Weber number and an impact parameter, we have identified a regime diagram that indicates the parametric conditions of different regimes, including other types of consequences specifically those show separation following temporary coalescence. While the outcome of interaction between two drops at rest can be analyzed by an approach of free energy, those with significant relative motions need to account for the impact inertia. Via an analysis based on conservation of energy, a model has been established to predict the critical Weber number of transition between two different regimes of merging.