Sammendrag
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.
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