Field-induced deformation and disruption of a planar water-oil interface under the influence of a conducting sphere

The deformation and instability of a planar interface between a conducting liquid and an insulating fluid under the action of a polarised metallic sphere is investigated with relevance to the problem of electrocoalescence of water droplets in oil. A theoretical study of the static interface deformation is performed in the case of a potential difference imposed between sphere and conducting liquid. The critical conditions are determined in the asymptotic case of very small sphere-interface separation. A preliminary experimental investigation has been carried out for the two cases water-air and water-oil with AC and DC applied voltage. The results are presented and compared with theoretical predictions. Finally the case of imposed field, which is important for the electrocoalescence of droplets in water-in-oil emulsions is briefly discussed.