Shape evolution of a water drop in asphaltene solution under weak DC electric fields

Abstract

The microscopic shape change of a pendent water drop, surrounded by an organic solution containing asphaltenes extracted from heavy crude oil, under electric field is investigated. Weak constant DC electric fields were applied in the direction perpendicular to gravity. The asphaltenes extracted from a heavy crude oil from Norwegian continental shelf were mixed in xylene at low concentrations. The simultaneous action of electric field and the asphaltene adsorption at the drop interface determines the shape of drop. Upon application of the electric field the drop exhibits instantaneous deformation in the direction of the field. Interestingly, the subsequent shape change occurs perpendicular to the field direction. The drop shape is observed to be asymmetric about both axes and the asymmetry intensifies with magnitude of the applied field and the concentration of asphaltenes in the surrounding medium. We thoroughly analyzed the temporal changes in shape features of the drop, which was held in the asphaltene solution for an hour. The influence of a range of concentrations and electric field strengths is investigated. The counter-intuitive shape development and the asymmetry are attributed to the electric field-reinforced asphaltene mass transport at the drop interface and the resultant interfacial properties.