Fluid dynamics of a double emulsion droplet in an electric field

Abstract

One of general free boundary problems concerning the electrohydrodynamic effects on a concentric double emulsion drop is studied theoretically for the three constituent phases of leaky dielectric fluids. In order to proceed the problem analytically, the domain perturbation procedure is utilized in the small deformation limit. The patterns of electric-field-driven flow are successfully characterized by examining the distribution of induced surface charges at the inner and outer drop interfaces. The second recirculating flow is generated in the annular phase when the inner and outer interfaces are charged with the same sense. The deformation type of inner and outer interfaces can be roughly interpreted by the flow patterns, although the exact description on the deformation requires consideration of the combined contributions from both electric and flow fields. In addition, the presence of double emulsion droplets alters the stress field of the continuous phase. The electric-field-induced ''particle stress'' not only changes the effective viscosity of dispersion of the double emulsion droplets but yields the normal stress difference, which is typical of a viscoelastic fluid. Finally, the heat transfer rate enhanced by the electric-field-driven flow is also considered. (C) 1999 American Institute of Physics. [S1070-6631(99)01605-0].