Electrocoalescence of water in oil emulsions: a DPD simulation study and a novel application of electroporation theory

Abstract

Pore formation in a surfactant laden oil film between two aqueous electrolyte layers in a DC field was studied using DPD (Dissipative Particle Dynamics molecular simulation). This setting represents the final stage of an electro-coalescence process between water droplets in oil, where the oil film has drained out to nanometer thickness. We introduce a novel model for the coalescence probability based on electroporation theory for lipid bilayers, and an equation for a threshold electric potential above which coalescence is highly probable. Excess electric forcing (pinching) of the oil film occurred locally due to charge density fluctuations in the electrolyte, and this could lead to the formation of unstable, expanding pores and coalescence between the aqueous domains. Such unstable pores can form at lower electric potentials when the cohesive energy in the surfactant layer (primarily line tension) is lowered by adding demulsifier, or when demulsifier causes a morphology change in the surfactant layers with local areas that have lower surfactant density. In conclusion, higher ion concentrations in the electrolyte, higher electric field strength, and lower cohesive energy in the surfactant layer increased the coalescence probability.