Rapid demulsification of dense oil-in-water emulsion by low external electric field.: II. Theory

Rapid demulsification of dense oil-in-water emulsions under external low electric fields was theoretically analyzed in the framework of the DLVO theory by solving the Smoluchowski diffusion equation for ions and the Poisson’s equation for electrostatic fields. The theory revealed that the applied field induces the demulsification according to the following mechanisms. (1) The applied field induces a steady-state current of ions in an aqueous phase, which in turn generates an electric field in the aqueous phase. (2) The electric field in the aqueous phase rearranges surface charges on oil droplets to compensate the field gradient on the surface of each droplet, which causes the polarization of the electrostatic surface potential. (3) The polarization lowers repulsive osmotic pressure in the overlapped diffuse electric double layers for the droplets, so that the demulsification is accelerated.