How Fluctuations Influence Barriers to Dewetting

Liquid water can become metastable with respect to its vapor under tension as well as in a variety of hydrophobic confinement contexts. The resulting dewetting transitions are often impeded by large free energetic barriers. According to macroscopic interfacial thermodynamics, such barriers arise from the free energy required to nucleate a critical vapor bubble — bubbles that are smaller than the critical bubble collapse, whereas larger ones grow spontaneously. Using molecular simulations in conjunction with enhanced sampling techniques, we have recently investigated the role of nanoscale water density fluctuations on dewetting barriers in three contexts: (i) cavitation or homogeneous nucleation under tension, (ii) capillary evaporation between two hydrophobic surfaces, and (iii) Wenzel-to-Cassie transition on textured surfaces. In each case, we find that 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 can involve a number of transitions between distinct dewetted morphologies, with each transition lowering the resistance to dewetting. Our results thus suggest a key role for fluctuations in speeding up the kinetics of numerous phenomena ranging from Cassie–Wenzel transitions on superhydrophobic surfaces, to hydrophobically driven biomolecular folding and assembly. They also help explain the experimentally observed tension that water can sustain before it spontaneously cavitates, and facilitate the design of novel surface textures capable of spontaneously recovering their superhydrophobicity.