On the influence of the intermolecular potential on the wetting properties of water on silica surfaces

TL;DR

This study uses molecular dynamics simulations to examine how different intermolecular potentials affect water's wetting behavior on silica surfaces, revealing the importance of electrostatic and van der Waals interactions in surface hydrophilicity.

Contribution

It compares two water-silica interaction models, showing how potential choice influences wetting properties and provides insights into the electrostatic and van der Waals contributions.

Findings

GT model predicts complete wetting at moderate pore filling, aligning with experiments.

Contact angle saturates around 2.5-3 nm slab thickness, matching experimental data.

Electrostatic interactions mainly determine surface hydroaffinity, with van der Waals effects also significant.

Abstract

We study the wetting properties of water on silica surfaces using molecular dynamics (MD) simulations. To describe the intermolecular interaction between water and silica atoms, two types of interaction potential models are used: the standard Br\'odka and Zerda (BZ) model, and the Gulmen and Thompson (GT) model. We perform an in-depth analysis of the influence of the choice of the potential on the arrangement of the water molecules in partially filled pores and on top of silica slabs. We find that at moderate pore filling ratios, the GT silica surface is completely wetted by water molecules, which agrees well with experimental findings, while the commonly used BZ surface is less hydrophilic and is only partially wetted. We interpret our simulation results using an analytical calculation of the phase diagram of water in partially filled pores. Moreover, an evaluation of the contact angle of the water droplet on top of the silica slab reveals that the interaction becomes more hydrophilic with increasing slab thickness and saturates around 2.5-3 nm, in agreement with the experimentally found value. Our analysis also shows that the hydroaffinity of the surface is mainly determined by the electrostatic interaction, but that the van der Waals interaction nevertheless is strong enough that it can turn a hydrophobic surface into a hydrophilic surface.