Mechanistic Insights into Emulsion Destabilization by Electric Fields.

Abstract

Although stable emulsions are often desirable, in some applications, they must be destabilized. One common approach is to apply electric fields to promote droplet coalescence, yet the underlying mechanisms remain poorly understood due to the sometimes subtle interplay of hydrodynamics, capillarity, intermolecular forces, and both interfacial and Maxwell stresses. Here, we use a modified dynamic thin film balance technique to simulate electrocoalescence in two types of systems, namely "surface active" and "rheologically active" interfaces. Despite their distinct stabilization mechanisms, we find that the key factor influencing electrocoalescence is the same in all cases: the local film thickness, which directly affects the magnitude of the Maxwell pressure. For nonionic surfactant films, we identify two distinct regimes: (i) a hydrodynamics-dominated regime, where relatively small electric pressures (∼Pa range) are sufficient to break the film, and (ii) a regime in which intermolecular forces stabilize the Newton Black Film, increasing the required breakup pressure to the ∼ kPa range. Asphaltene-laden films, in the limit of insoluble interfaces, form a representative example of rheologically complex interfaces. We find that elastic properties stabilize these films at significantly larger thicknesses, rendering electric fields ineffective─unless demulsifiers are introduced to promote local heterogeneity and thinning. This study provides new insight into how electrostatic fields destabilize emulsions and suggests new avenues for developing more efficient destabilization strategies.