Electrocoalescence of Two Drops with Different Surfactant Concentrations Suspended in Oil

In this study, the electrocoalescence characteristic of two drops with different surfactant concentrations suspended in oil is revealed. Different from the symmetrical coalescence of identical drops, the asymmetrical liquid bridge is induced by the capillary force, which involves the interfacial tension gradient between the drops. In addition, a mushroom-like jet is formed during asymmetrical coalescence, causing mixing of drops. A characteristic time considering the interfacial tension gradient is proposed to describe the asymmetrical liquid bridge evolution. The mushroom-like jet is found to be driven by the pressure difference between drops, which has a positive correlation with the interfacial tension gradient. Moreover, it is found that the electrocoalescence time is shortened as the interfacial tension increases. This study indicates that increasing the interfacial tension gradient will enhance the jet flow rate and reduce the coalescence time, which is of significance to improve the mixing efficiency of the drops.