Destabilization of Pickering emulsions using external electric fields.

It is known that emulsions can be stabilized by the presence of particles that get trapped at fluid-fluid interfaces and prevent adjacent drops from coalescing with one another. We show here that such emulsions, or Pickering emulsions, can be destabilized by applying external electric fields. This is demonstrated experimentally by studying water drops in decane and silicone oil drops in corn oil in the presence of micro-sized particles. It is shown that the primary phenomenon responsible for the destabilization is the motion of particles on the surface of drops in the presence of a uniform electric field. Although there should be no electrostatic forces acting on neutral particles in a uniform electric field, the presence of the drop itself introduces nonuniformity, which leads to dielectrophoretic forces acting on the particles and is thus responsible for particle motions along the drop surface. Particles translate to either the poles or the equator of the drop, depending on the relative dielectric constants of the particles, the surrounding fluid and the fluid within the drop. Such motions break the particle barrier, thus allowing for drops to merge with one another and therefore destabilizing the emulsion.