Phase transition of water–in–oil emulsions over influence of an external electric field

Barker–Henderson perturbation theory for the fluid-like phase and van der Waals theory for the solid-like phase were used to calculate phase diagrams of water-in-crude oil emulsions over influence of an external electric field. The effective interaction potential between water droplets was calculated as a sum over a steric repulsive, an attractive dispersion, and dipole–dipole interactions. In order to calculate the dipole–dipole attractive interaction, that appears when an external electric field is applied, we used an angular averaged potential that gives the Keesom approximation at high temperatures and/or at low electric fields. The results indicate that droplets polarization due to the external electric field yields to the occurrence of fluid–fluid transition, that is metastable for low electric field and becomes stable when the dipole–dipole attractive interaction is dominant (i.e., at high electric field).