Rapid demulsification of dense oil-in-water emulsion by low external electric field: I. Experimental evidence

Rapid demulsification of dense oil-in-water (O/W) emulsions has been found to be induced by applying a low electric field of the order of 1–10 V/cm. The demulsification simultaneously takes place over the entire space between two electrodes. Dilute O/W emulsions are demulsified only near an electrode after being condensed by electrophoresis of the droplets, which indicates that the mutual contact of oil droplets through thin water layers is necessary for the rapid demulsification. Increase of the concentration of electrolyte accelerates the demulsification, whereas increase of the concentration of an ionic surfactant retards the demulsification. O/W emulsions stabilized with a nonionic polymer surfactant are not demulsified. Water-in-oil (W/O) emulsions are not demulsified even the chemical components are the same as those of the O/W emulsion. Application of an alternating electric field with the frequency higher than 10 kHz does not cause the demulsification. All this evidence strongly suggests that the applied low electric field causes the rearrangement of surface charges on oil droplets, which results in the reduction of the height of an energy barrier for the coalescence of the droplets.