  Liquid drops on textured surfaces show different dynamical behaviors
depending on their wetting states. They are extremely mobile when they are
supported by composite solid-liquid-air interfaces (Cassie-Baxter state) and
immobile when they fully wet the textured surfaces (Wenzel state). By
reversibly switching between these two states, it will be possible to achieve
large control over the fluid dynamics. Unfortunately, these wetting transitions
are usually prevented by surface energy barriers. We demonstrate here a new and
simple design paradigm, consisting of parallel grooves of appropriate aspect
ratio, that allows for a controlled, barrierless, and reversible switching of
the wetting states upon the application of electrowetting. We report a direct
observation of the barrierless dynamical pathway for the reversible transitions
between the Wenzel (collapsed) and the Cassie-Baxter (suspended) states and
present a theory that accounts for these transitions, including detailed
lattice-Boltzmann simulations.
