Interface Modeling for the Ab Initio Evaluation of the Water Contact Angle on a Metallic Cu(111) Surface

Abstract

Controlling the water contact angle on a surface is important for regulating its wettability in industrial applications. Therefore, it is crucial to develop ab initio evaluation methods that can accurately predict this angle. The ab initio predictions require an adsorption structure model for the adsorption of liquid molecules on a surface, but the construction of this model depends on whether the test surface comprises an insulating or metallic material because the surface reconstruction takes quite a different form in each case. Previous studies have focused on the estimation of the water contact angle on insulators; however, this study elucidates the water contact angle on a metallic surface, Cu(111). Because the feasibility of ab initio evaluations depends on the approximation of liquid–gas interface energy, which can be roughly estimated through the interface energy of crystal ice, it is natural to use the periodic-honeycomb array of water molecules as the adsorption model for the water on the surface. However, despite the successful application of the periodic model for ab initio prediction of the water contact angle on insulating surfaces, applying this model to metallic surfaces has not provided satisfactory predictions that reproduce experimental values. Therefore, in this study, we propose the use of models with isolated water oligomers for the ab initio prediction of the water contact angle on a metallic surface, which achieved an accurate prediction. The ambiguity of the models based on the size and coverage of the oligomers was small (∼ ±10 °), which was averaged out to give a plausible value based on the Boltzmann weight with the adsorbing energies. The proposed procedure can be used to estimate the wettability of the surfaces of other metallic materials.