Effects of impact and fluid properties on endocytosis-like entrainment during immiscible droplet impact

Droplet impact on immiscible liquid pools can produce diverse interfacial responses, including jetting, splashing, rebound, and liquid entrainment. Our recent research identified an endocytosis-like mode in which a portion of the pool liquid enters the impacting droplet and becomes isolated as an internal core. However, changing the experimental fluid pair generally alters several properties simultaneously, making the individual roles of the governing physical parameters difficult to identify. Here, we adopt axisymmetric three-phase simulations to independently investigate the effects of impact velocity, droplet viscosity, pool viscosity, and droplet–pool interfacial tension. The simulations show that these parameters affect the extent and timing of droplet–pool interfacial deformation in different ways and result in distinct outcomes. Increasing impact velocity promotes central-column development and drives the outcome from no pinch-off to regular and eventually complex entrainment. Increasing either droplet or pool viscosity weakens the column response and basal contraction, but their temporal effects differ, with pool viscosity delaying the overall evolution yet droplet viscosity advancing the characteristic response times. Increasing droplet–pool interfacial tension mainly accelerates the interfacial evolution and favors sustained basal contraction, while weakly changing the established column height. Dimensionless regime maps based on the Weber number and Ohnesorge numbers further organize the transitions among the observed entrainment outcomes. These results clarify how impact inertia, viscosity, and interfacial tension jointly govern endocytosis-like entrainment in immiscible liquid systems.