Electrophoretic motion of a charged water droplet near an oil-air interface

Abstract

The trajectory of a charged droplet near an oil-air interface is investigated. When a charged droplet is translated in oil by electrophoresis, the droplet follows a straight line between two electrodes. However, if an oil-air interface is close to a droplet, the droplet follows an upwardly concave parabolic pathway. By using the leaky dielectric model, we have verified that this phenomenon is caused by the distorted electric field due to the difference in permittivities. Furthermore, it is enhanced by the accumulated free charges on the oil-air interface due to the difference in the electric conductivities of oil and air. Finally, we suggest a complementary arrangement of electrodes for realizing a straight pathway of the droplet near the interface. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4723633]