Roughness-Induced Wetting

TL;DR

This paper theoretically explores how geometric roughness on a solid substrate can induce wetting transitions that do not occur on flat surfaces, using a novel interaction model and harmonic approximation.

Contribution

It introduces a new closed-form expression relating sinusoidally modulated interface interactions to flat interface interactions, revealing conditions for roughness-induced wetting.

Findings

Roughness can induce wetting if substrate surface area exceeds a threshold.

Wetting potential must have a pronounced maximum at certain separations.

Results align with experimental observations of surface premelting phenomena.

Abstract

We investigate theoretically the possibility of a wetting transition induced by geometric roughness of a solid substrate for the case where the flat substrate does not show a wetting layer. Our approach makes use of a novel closed-form expression which relates the interaction between two sinusoidally modulated interfaces to the interaction between two flat interfaces. Within the harmonic approximation, we find that roughness-induced wetting is indeed possible if the substrate roughness, quantified by the substrate surface area, exceeds a certain threshold. In addition, the molecular interactions between the substrate and the wetting substance have to satisfy several conditions. These results are expressed in terms of a lower bound on the wetting potential for a flat substrate in order for roughness-induced wetting to occur. This lower bound has the following properties: A minimum is present at zero or very small separation between the two interfaces, as characteristic for the non-wetting situation in the flat case. Most importantly, the wetting potential needs to have a pronounced maximum at a separation comparable to the amplitude of the substrate roughness. These findings are in agreement with the experimental observation of roughness-induced surface premelting at a glass-ice interface as well as the calculation of the dispersion interaction for the corresponding glass-water-ice system.