We investigate directly at the microscale the morphology of the electrowetting induced transition between the Cassie-Baxter and Wenzel states for a water droplet on a superhydrophobic surface. Our experiments demonstrate that the transition originates in a very narrow annular region near the macroscopic contact line, which is first invaded by water and causes a thin film of air to be entrapped below. At high applied voltages, a growing fraction of microscopic air-pockets collapse, resulting in a partialWenzel state. Modulations in the intensity of the light reflected from individual micro-menisci clarify that the local contact angles near the filling transition are close to the usual advancing values for contact lines on smooth surfaces.
@article{arxiv.0801.2683,
title = {Microscopic structure of electrowetting-driven transitions on superhydrophobic surfaces},
author = {A. Staicu and G. Manukyan and F. Mugele},
journal= {arXiv preprint arXiv:0801.2683},
year = {2008}
}