Electric-field–driven instabilities on superhydrophobic surfaces

We study possible mechanisms of the transition from the Cassie state to the Wenzel state on superhydrophobic surfaces under the influence of electric fields as a function of the aspect ratio and the wettability of the surface. A simple analytical model for axisymmetric cavities and small deflections of the liquid menisci within the cavities reveals the existence of a novel electric-field–driven instability of the liquid surface. Fully self-consistent calculations of both electric-field distribution and surface profiles show that this instability evolves from a global one towards a local Taylor cone-like instability for increasing aspect ratio of the cavities. A two-dimensional map is derived indicating the prevalence of the interfacial instability as compared to the depinning scenario of the three-phase contact line, which is well known from ordinary superhydrophobic surfaces.