Possibility of coalescence of water droplets in W/O emulsions by means of surface processes

It is interesting to examine from a scientific viewpoint whether surface processes can bring about coalescence of droplets of emulsions (de-emulsions) in the context that de-emulsification is a bulk process rather than a surface one. The de-emulsification by electrode processes and surface catalysis was here applied to water-in-oil emulsions, which are models of water-included petroleum. When DC-voltage was applied to the emulsions composed of salt-included water droplets, current was observed only for the volume fraction of water more than 0.23. This value was regarded as a threshold of the electric percolation. A long-time electrolysis made water droplets coalesce only on the electrode surface, and hence did not lead to de-emulsification in the bulk. We found by a microscope that a hydrophilic glass surface worked as a catalyst of de-emulsification. The de-emulsification was caused by the adsorption of droplets on the glass plate to be flattened. The probability of the de-emulsification was proportional to the volume fraction of the water. It was explained in terms of the model of random collision of droplets on a plane. The adsorption and flattening were applied to removal of water droplets from the emulsions by adding hydrophilic glass powder to the emulsions.