Interface instability induced by an electric field in fluids

An interface between two immiscible, nonionic fluids becomes unstable if an electric field is applied and if the angle between the field and the interface normal is smaller than a critical angle. We do not assume the presence of ions on the interface in contrast to previous work. The characteristic wave number k* of the undulations is proportional to the square of the field and inversely proportional to the surface tension. We also show that a thin layer on a capacitor plate loses its stability more easily than an interface far from the plates. New effects can be expected in near-critical fluids, in which the surface tension is small and k* can be much larger than the inverse of the capillary length. Moreover, k* ultimately exceeds the inverse of the correlation length very close to the critical point, where the critical behavior and the domain structure are drastically altered by electric field.