Spontaneous Recovery of Superhydrophobicity on Nano-Textured Surfaces

Surface texture can render hydrophobic surfaces into superhydrophobic, and endow them with properties like water-repellency, self-cleaning, interfacial slip, and fouling resistance. Superhydrophobicity stems from the reluctance of water to penetrate the surface texture, so that a water droplet resides on top of a cushion of air, making contact with only the tips of the rough hydrophobic surface in a so-called Cassie state. A major impediment in the widespread industrial adoption of superhydrophobic surfaces is the loss of superhydrophobicity upon the wetting of the surface texture, yielding the wet Wenzel state. Moreover, this loss of superhydrophobicity is widely considered irreversible due to the presence of large kinetic barriers that impede the Wenzel-to-Cassie transition. We use atomistic simulations to demonstrate that wetting on nano-pillared surfaces follows a fluctuation-mediated dewetting pathway involving a number of transitions between distinct dewetted morphologies. Such a non-classical pathway leads to reduced dewetting barriers and a finite, albeit low extrusion pressure at which system can spontaneously dewet. Using insights from the dewetting pathway on the nano-pillared system, we are able to design novel surface textures on which the Wenzel state has been rendered unstable, and superhydrophobicity can be spontaneously recovered under ambient conditions.