Wetting regimes and interactions of parallel plane surfaces in a polar liquid

TL;DR

This paper uses a phenomenological model to analyze how polar liquids mediate interactions between parallel surfaces, revealing regimes of attraction and repulsion based on surface properties and predicting a new intermediate interaction regime.

Contribution

It introduces a theoretical framework for understanding polar liquid interactions with surfaces, identifying distinct regimes based on surface hydrophobicity and hydrophilicity, including a novel intermediate regime.

Findings

Hydrophobic surfaces induce long-range attractive interactions.

Hydrophilic surfaces cause short-range repulsive interactions.

An intermediate regime with weak, inverse-square decay interaction is predicted.

Abstract

We apply a phenomenological theory of polar liquids to calculate the interaction energy between two plane surfaces at nm-distances. We show that depending on the properties of the surface-liquid interfaces, the interacting surfaces induce polarization of the liquid in different ways. We find, in full agreement with available experiments, that if the interfaces are mostly hydrophobic, then the interaction is attractive and relatively long-ranged (interaction decay length \lambda\sim1.2\, nm). The water molecules are net polarized parallel to the surfaces in this case. If the surfaces are mostly hydrophilic, then the molecules are polarized against the surfaces, and the interaction becomes repulsive, but at a short-range (\lambda\sim0.2\, nm). Finally, we predict there exists an intermediate regime, where the surfaces fail to order the water molecules, the interaction becomes much weaker, attractive and, at relatively small distances, decays with the inverse square of the distance between the surfaces.