Influence of surfactant on drop deformation in an electric field

Abstract

The deformation of a surfactant-covered, viscous drop suspended in a viscous fluid under the influence of an electric field is investigated using numerical simulations. The full Navier–Stokes equations are solved in both fluid phases, and the motion of the interface and the interfacial discontinuities are handled using the level-set method. The leaky-dielectric model is used to take into account the effect of an electric field. The surfactant is assumed to be insoluble, and an evolution equation for the motion of surfactant is solved along the drop surface. The surfactant concentration and the interfacial tension are coupled through a nonlinear equation of state. The numerical results show that the effect of surfactant strongly depends on the relative permittivity and conductivity between the fluids. The presence of surfactant can both increase and reduce the deformation, depending on the shape of the deformation and the direction of the electrically induced circulation.