Electro-capillary instabilities of thin leaky elastic-viscous bilayers

Abstract

Electrohydrodynamic stresses originating from the accumulation of free and induced charges at the confined interface of a thin elastic-viscous bilayer composed of weakly conducting elastic or viscous films can stimulate permanent micropatterns such as creases, wrinkles, holes, and columns. We show that a complete linear stability analysis including all the leading order terms from the Maxwell stresses can accurately predict the key short to long-wave transitions in the length scales, as reported recently by the experimental studies. The generic potential employed for the electric field in the present work overcomes the limitations of the existing theories, which could not precisely predict the length scales especially in the short-wave limit. Importantly, unlike the experimentally reported configuration with a dielectric elastic layer confined by a weakly conducting liquid layer, the bilayers with a weakly conducting elastic layer confined by a dielectric liquid layer can develop interfacial patterns with similar periodicity at smaller field intensity. The transitions from long- to short-wave are compared and contrasted for the bilayers with leaky elastic or viscous films by tuning the field intensity, interfacial tension, and thicknesses of the films. The study unveils that the charged interface of a leaky confined bilayer experiences a larger stress due to the accumulation of free and bound charges, which can significantly reduce the length scales of the instability to the sub-micron regime. The results reported can stimulate further investigation related to the patterning and miniaturization exploiting the field induced instabilities of the elastic films.