  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.
