Effects of Applied DC Electric Fields on Water-Oil Interfacial Properties

Abstract

Among all the competing methods to enhance the phase separation of water-in-oil emulsions in chemical industries, electric field is considered as one of the best treatment options. To better understand the mechanism by which electric field assists water droplets coalescence and the corresponding physics of skin formation, the interfacial properties of the water/oil interface in a water-in-model oil emulsion system, including interfacial tension, shape factor, crumpling ratio and dilatational rheology, are studied with a tensiometer. The pendant water drop deforms immediately at the onset of electric field application, into either a prolate shape or an oblate shape in the direction of electric field, depending on the properties of the continuous phase. The degree of drop deformation is of positive correlation with the experienced electric field strength and is also affected by the electric field direction and the drop position in between the electrodes. An external electric field is found to enhance the formation of interfacial asphaltene layer elucidated by a higher crumpling ratio, lower interfacial tension, higher shape factor and higher elasticity with increasing electric field strength. This could be due to the induced electrohydrodynamic flow, which triggers the interfacial convection and accelerates asphaltene movements and adsorption. The same trend holds true for measurements with various asphaltene concentration, aging time, water phase pH, and water salinity under electric field application. Although the electric-assisted formation of a stronger interfacial barrier is against drop-drop coalescence, a hypothesis is proposed that the electric-induced drop deformation may dominant, enlarging the interfacial area and generating a patchy film with weak spots for easier drop-drop coalescence.