Electric field induced instabilities of thin leaky bilayers: pathways to unique morphologies and miniaturization.

Charge leakage of the weakly conducting liquid layers in a thin bilayer can engender interesting interfacial instabilities when exposed to an external electrostatic field. A general linear stability analysis including the full descriptions of the Maxwell stresses uncovers the key short to long-wave features of the instabilities of the bilayers composed of purely dielectric films, leaky dielectric films, and a combination of leaky and dielectric films. The study highlights that for the leaky bilayers the additional electrostatic stress due to the presence of free charges at the interface(s) can significantly reduce the length scale to enforce pattern miniaturization. Unlike a purely dielectric bilayer where the dielectric-contrast across the interfaces dictates the direction of the interfacial deformations, for leaky bilayers the nature of the charge (positive or negative) at the interface can also contribute to the deformation towards or away from the electrodes (anode or cathode). Nonlinear simulations uncover that the interfaces can develop unique morphologies when the spatiotemporal variation of the attractive or repulsive force at the charged interface act together or against the electrical stress due to the induced charge separation across the interface. Exploiting these features a host of periodic interfacial patterns such as core-shell columns, a hole encapsulated by a column, a bundle of columns embedded inside a single column, a collection of holes embedded under a column, and "caged" columns are obtained, which are rather difficult to assemble using other conventional patterning techniques. The results reported can be of importance in the diverse areas of micro/nanotechnology.