(57d) Molecular Mechanism of Dewetting in Hydrophobic Confinement

Water near extended hydrophobic surfaces sits at the edge of a dewetting transition and is sensitive to perturbations. Such a perturbation is most readily provided by the presence of another hydrophobic surface nearby, so that when two such extended hydrophobic surfaces approach each other, water between them becomes metastable with respect to its vapor. While the inter-surface separation at which water becomes metastable can quite large (~100 nm), large kinetic barriers separating the metastable wet and the stable dry states prevent the dewetting transition, which is triggered only at much smaller separations (~1 nm). Previous simulation and numerical modeling studies suggest that the transition state corresponds to a roughly cylindrical critical vapor tube spanning the region between the surfaces. Using specialized molecular simulations, we estimate the free energetics of the dewetting process for a range of inter-plate separations with the inter-plate water density as the order parameter. Our findings point to the importance of enhanced water density fluctuations adjacent to the individual hydrophobic surfaces in the dewetting process and suggest the existence of a novel dewetting mechanism for certain inter-plate separations.