Hydration structure on crystalline silica substrates.

The structure of interfacial water at the silica solid surfaces was investigated using molecular dynamics simulations. Different degrees of surface hydroxylation were employed to assess the effect of the surface chemistry on the structure of interfacial water. Density profiles, in-plane radial distribution functions, in-plane density distribution, and hydrogen-bond profiles were calculated. Our results show that the surface hydroxylation affects the structure, orientation, and hydrogen-bond network of interfacial water molecules. Data analysis suggests that the degree of hydroxylation controls the amount of water molecules in the first interfacial layer as well as the distance between the first adsorbed layer and the substrate. Well-organized and uniform structures of interfacial water appear on the homogeneously hydroxylated surface, while a heterogeneous interfacial structure, characterized by extensive water-water hydrogen bonds, forms on the partially hydroxylated surface. We demonstrate that both the local surface chemistry and water-water hydrogen bonds are the dominant factors that determine the structural properties of interfacial water.