Instability and drop formation of liquid-liquid interface under electric field

The effect of electric field on behavior of the interface of stratified water and silicone oil has been studied experimentally. A positive plate electrode of 80×80 mm2, apart 30∼80 mm from the interface, is installed in the oil located on water, and negative one in water. The interface becomes unstable by applying high voltage between electrodes, and the waves on the interface are generated. The drops are generated from the wave above a certain applied voltage. The phenomena of wave generation and drop formation are taken with the high-speed video camera, and analyzed. As a result, the range of an applied voltage to generate the drop exists when the distance from liquid-liquid interface to the positive plate electrode is more than 30 mm. Two types are admitted in the drop formation from the waves, and great difference is seen by the type in wave hight and drop diameter. One may have the same mechanism similar to an electrostatic atomization that makes drops of small diameter. For another one, cone-wise waves expanded by the influence of the electric field become unstable, and collapse to make drops of larger dimeter. It is clarified that the wave height expands when two or more waves are composed in the electric field.