The molecular structure of the interface between water and a hydrophobic substrate is liquid-vapor like

TL;DR

This study uses molecular simulation to compare water interfaces with hydrophobic and hydrophilic surfaces, revealing that hydrophobic interfaces resemble liquid-vapor interfaces, while hydrophilic ones disrupt hydrogen bonding networks.

Contribution

It demonstrates that water-hydrophobic interfaces are structurally similar to water-vapor interfaces, unlike water-hydrophilic interfaces, providing new insights into interfacial molecular structure.

Findings

Hydrophobic interactions minimally affect intrinsic interface structure.

Attractive interactions influence capillary wave fluctuations.

Hydrophilic surfaces disrupt hydrogen bonding networks.

Abstract

With molecular simulation for water and a tunable hydrophobic substrate, we apply the instantaneous interface construction [A. P. Willard and D. Chandler, J. Phys. Chem. B, 114, 1954 (2010)] to examine the similarity between a water-vapor interface and a water-hydrophobic surface interface. The intrinsic interface refers to molecular structure in terms of distances from the instantaneous interface. We show that attractive interactions between a hydrophobic surface and water affect capillary wave fluctuations of the instantaneous liquid interface, but these attractive interactions have essentially no effect on the intrinsic interface. Further, the intrinsic interface of liquid water and a hydrophobic substrate differs little from that of water and its vapor.The same is not true, we show, for an interface between water and a hydrophilic substrate. In that case, strong directional substrate-water interactions disrupt the liquid-vapor-like interfacial hydrogen bonding network.