Intrinsic water layering next to soft, solid, hydrophobic, and hydrophilic substrates.

ABSTRACT

How a substrate modulates properties of water upon it and how far the perturbation is present remain to be fundamental questions in surface science. To answer these questions, we develop a layer-by-layer exfoliation method to identify physically meaningful water layers upon a substrate through molecular dynamics simulations under ambient conditions. The results show a qualitatively consistent long-ranged layer-by-layer propagation of the atomic structure, irrespective of whether the substrate is soft, solid, hydrophobic, or hydrophilic. The capillary-wave fluctuation of a water layer upon air or oil diverges with long wavelength but is truncated upon solid substrates by an effective field, which exhibits a long-ranged decay but its strength is almost irrelevant with substrate chemistry. The distinction in the water structure and atomic dynamics due to substrate specificity is mostly limited to the outmost layer. We conclude a long-ranged layering organization and a short-ranged substrate-dependent specificity for interfacial water.