(253bg) Understanding Wetting-Dewetting Transitions on Nanotextured Surfaces: Implications for Designing Surfaces with Robust Superhydrophobicity

Owing to a water contact angle greater than 150° and an effortless rolling off of water droplets, superhydrophobic surfaces exhibit self-cleaning, drag reducing and anti-icing properties. Such qualities of superhydrophobic surfaces make them revolutionary materials desired in myriad industrial applications and have spurred the discovery of numerous ways for texturing hydrophobic surfaces. It is now well established that superhydrophobicity derives from texturing of hydrophobic surfaces; the aversion of water for the hydrophobic surface prevents wetting of the surface texture, and stabilizes a Cassie state, in which a water droplet resides on the tips of the surface asperities. However, a key bottleneck in the widespread adoption of superhydrophobic surfaces has been the irreversible loss of superhydrophobicity, a consequence of wetting of the surface texture into a non-functional Wenzel state, under a variety of conditions ranging from elevated pressure and temperature to condensation of water in the texture. Furthermore, this wetting of the surface texture i.e the loss of superhydrophobicity is widely believed to be irreversible due to the large energy barriers that prevent the reverse (dewetting) transition. By using molecular dynamics simulations to characterize the free energetics and pathways of transition between the Cassie and the Wenzel states, our work strives to understand wetting-dewetting transitions on textured surfaces on a molecular level. Importantly, we illustrate how an understanding of dewetting pathways can inform the design of novel surface textures on which dewetting barriers vanish and superhydrophobicity can be spontaneously recovered. Such robust superhydrophobic surfaces, identified here for the first time, could find widespread application even under the most challenging conditions such as underwater operation or condensation heat transfer applications.