Boundary-element calculations for dielectric relaxation of water-in-oil-in-water emulsions consisting of spherical droplets with a spheroidal core

Using the boundary-element method, theoretical calculations were made for the complex permittivity of water-in-oil-in-water emulsions consisting of spherical droplets. A spheroidal inner phase was placed at the center of the droplet. To examine the effects of the shape of the inner phase, the axial ratio of the inner phase was changed by keeping its volume unchanged. The results showed that the dielectric relaxation of the emulsions was markedly affected by the shape of the inner phase. As a detailed analysis, effects of external electric fields directed in the mirror plane and those along the rotation axis of the droplets were examined separately. This showed that the relaxation consisted of two kinds of relaxation terms. The first related to the structure of the droplet parallel to the external field and had similar character to the low-frequency relaxation of emulsions of shelled spheres. The second, found in restricted cases, related to the structure perpendicular to the external field, having character similar to the high-frequency relaxation for the shelled spheres. Received: 8 May 2001 Accepted: 29 August 2001