The collision of immiscible droplets in three-phase liquid systems: A numerical study using phase-field lattice Boltzmann method

Abstract

A ternary phase-field LB model was employed in this paper to study the collision between two immiscible liquid droplets in a continuous liquid medium. Five different cases were considered based on droplets’ density, viscosity, and interfacial tension ratio. The results were presented in the form of We-B. (Weber number, and collision parameter) nomograms. The hydrodynamics of the interaction was analyzed by visualizing droplets’ deformation and behavior during the impact, especially in the contact area. Three collision outcomes were identified for both partial and total spreading states: engulfment (I), bounce (II), and engulfment with encapsulation of a tiny bulk liquid drop (III). The highest probability of the latter was seen at We > 50 and B < 0.5 for the cases in which droplets had equal density and viscosity. It was found that the satellite droplet encapsulation in regime (III) occurs for the deformed droplets as a result of a concave interface at the moment of contact. This in turn leads to the formation of two contact points and liquid bridges. No satellite formation was observed for the case where the density ratio between the droplets was relatively high. Moreover, a drastic decrease (≈35%) in the boundary between regimes (II) and (I) was observed in this case, compared to the cases where the interacting droplets had equal density. Performed simulations for collisions near the transition point from partial to complete engulfment revealed that the hydrodynamics of interaction and the collision regimes are similar in both cases, despite the difference in the final morphology of the compound.