Dewetting Transitions on Superhydrophobic Surfaces: When Are Wenzel Drops Reversible?

On
superhydrophobic surfaces, drops in the Wenzel state can be
switched to the suspended Cassie state in some cases but in other
cases are irreversibly impaled in the surface roughness. To date,
the question of when dewetting transitions are possible for Wenzel
drops has not been resolved. Here, we show that pinned Wenzel drops
being stretched out-of-plane cannot reduce their contact angle below
a critical value where unstable pinch-off occurs, preventing dewetting
for Wenzel drops that exhibit receding contact angles beneath this
critical pinch-off angle. Dewetting transitions are therefore only
possible for Wenzel drops with moderately large receding contact angles
(θr ≈ 90°), which requires low surface
roughness for one-tier surfaces or a Partial Wenzel wetting state
for two-tier surfaces.