Rough or textured hydrophobic surfaces are dubbed "superhydrophobic" due to their numerous desirable properties, such as water repellency and interfacial slip. Superhydrophobicity stems from an aversion of water for the hydrophobic surface texture, so that a water droplet in the superhydrophobic "Cassie state" contacts only the tips of the rough surface. However, superhydrophobicity is remarkably fragile and can break down due to the wetting of the surface texture to yield the "Wenzel state" under various conditions, such as elevated pressures or droplet impact. Moreover, due to large energetic barriers that impede the reverse transition (dewetting), this breakdown in superhydrophobicity is widely believed to be irreversible. Using molecular simulations in conjunction with enhanced sampling techniques, here we show that on surfaces with nanoscale texture, water density fluctuations can lead to a reduction in the free energetic barriers to dewetting by circumventing the classical dewetting pathways. In particular, the fluctuation-mediated dewetting pathway involves a number of transitions between distinct dewetted morphologies, with each transition lowering the resistance to dewetting. Importantly, an understanding of the mechanistic pathways to dewetting and their dependence on pressure allows us to augment the surface texture design, so that the barriers to dewetting are eliminated altogether and the Wenzel state becomes unstable at ambient conditions. Such robust surfaces, which defy classical expectations and can spontaneously recover their superhydrophobicity, could have widespread importance, from underwater operation to phase-change heat transfer applications.Cassie | Wenzel | dewetting | fluctuations | barriers S urface roughness or texture can transform hydrophobic surfaces into "superhydrophobic" surfaces and endow them with properties such as water repellency, self-cleaning, interfacial slip, and fouling resistance (1, 2). Each of these remarkable properties stems from the reluctance of water to penetrate the hydrophobic surface texture, so that a drop of water sits atop an air cushion in the socalled Cassie state, contacting only the top of the surface asperities. However, water can readily penetrate the surface texture, yielding the Wenzel state (3, 4) at elevated pressures (4, 5) or temperatures (6), upon droplet impact (7,8), as well as due to surface vibration (9), localized defects (10), or proximity to an electric field (11); superhydrophobicity is thus remarkably fragile and can break down due to the wetting of the surface texture under a wide variety of conditions. To facilitate the recovery of superhydrophobicity and to afford reversible control over surface properties, significant efforts have focused on inducing the reverse Wenzel-to-Cassie dewetting transition. However, a true Wenzel-to-Cassie transition has been elusive (12), with most reported instances making use of trapped air (11,(13)(14)(15) or generating a gas film using an external energy source (16, 17) to jump-start the dewetting...
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