Numerical investigations of electric field-mediated active droplet transfer in a ternary phase system

Abstract

A method of active transport of a droplet from a carrier liquid to a target liquid is proposed with the aid of an electric field. Numerical investigations shed light on the dynamics associated with the active migration of a water droplet across the interface of two weakly conducting oils via application of an electric field. With the aid of two model ternary liquid systems, two modes of droplet transfer are identified—(i) the film drainage mode and (ii) the tailing mode. In the film drainage mode obtained for the model system of silicone oil–water–oleic acid, at low electric fields, the water droplets undergo negligible distortions in shape and the film drainage and rupture occur in a quasi-steady manner. At higher fields, the droplet distorts into a prolate with unsteady drainage and the film rupture. The rate of film drainage increases with the strength of the applied electric field. The tailing mode of droplet transport is achieved for very low interfacial tension between the carrier and the target liquids. For the model system of silicone oil–water–soybean oil, in the tailing mode, the droplet entrains carrier liquid approximately equal to 4.5 times its own volume into the target liquid with the length of the tail as high as eight times the drop radius. The interfacial tensions of the liquid pairs, densities, viscosities, and dielectric constants of the liquids comprising the ternary system are the key parameters influencing the dynamics of migrations. The phenomena may find applications in liquid–liquid extraction, micro-reactions, and ultra-low tensiometry.