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 of the texture), this breakdown in superhydrophobicity is widely believed to be irreversible. Using molecular simulations and enhanced sampling techniques, we challenge this conventional wisdom. In particular, we show that water density fluctuations play an important role in dewetting the surface texture; by circumventing the classical dewetting pathways, fluctuations lead to a reduction in the free energetic barriers 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.

Rational design of nanotextured surfaces capable of spontaneously recovering their superhydrophobicity

254th National Meeting (2017)

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