Electrophoretic Behavior of Droplets Manipulated by Charging and Electrode Modification

The efficient removal of dispersed water droplets from water-in-oil emulsions remains a major challenge in petrochemical separation. Unlike conventional coalescence based on dipole interactions under alternating electric fields, this work proposes an enhanced DC electrophoretic coalescence strategy combining droplet charge enhancement and electrode surface modification to regulate the migration, capture, and coalescence of charged droplets. The results show that, in the parallel-plate electrode system, increasing the electric field intensity promoted droplet charging and electrophoretic migration, increasing the droplet surface charge density from the natural charging level of the 10-7 to 10-5 C/m2 level after contact charging. To further overcome this limited charge level, a needle-ring electrode charging method was developed, increasing the droplet surface charge density to the 10-4 C/m2 level and strengthening the electrophoretic driving force. However, direct contact between charged droplets and bare electrodes caused charge exchange, polarity reversal, and rebound, leading to repeated back-and-forth migration. To convert the enhanced electrophoretic migration into effective coalescence, electrode surface insulation was introduced. By suppressing rapid charge exchange between droplets and the metal electrode, the insulated electrode enabled charged droplets to be directionally captured, slide along the electrode surface, and coalesce with neighboring droplets. These results indicate that droplet charge enhancement and electrode-interface regulation can effectively promote electrophoretic migration and directional coalescence under a DC electric field, providing guidance for the design of efficient DC electrostatic coalescers.