Film drainage mechanism between two immiscible droplets

The interaction between two deformable droplets consists of unique dynamic characteristics that are not present during the interaction of solid bodies. A thin film of surrounding fluid is entrapped between the droplets and then drains out under the influence of an external force before the droplets can adhere or coalesce. The drainage process during the coalescence of two similar droplets has received significant research interest due to the presence of dynamical interactions between the droplets. Surprisingly, the film drainage process between two partial engulfing immiscible droplets has not been studied yet. Using a numerical study, we investigate the film drainage between two partial engulfing immiscible droplets. We vary the interfacial tensions between the droplets and surrounding fluid in wide ranges to observe the film drainage time between the droplets. Based on our simulations, we identified three regimes of fast, intermediate and delayed drainage. We found that the film drainage of two immiscible droplets exhibits additional flow into or out of the film, which does not exist in the film drainage of identical droplets. This additional flow can either increase or decrease the rate of film drainage between the droplets, depending on the interfacial tension of droplets with the surrounding fluid and the interfacial tension of the two immiscible droplets.