Interfacial Properties of the Nitrogen + Water System in the Presence of Hydrophilic Silica

The interfacial properties of the N₂ + H₂O and N₂ + H₂O + silica systems were investigated (in the temperature range of 313-448 K and at pressures up to 50 MPa) by using extensive molecular dynamics simulations. The simulated interfacial tension (IFT) of the N₂ + H₂O system is in line with our density gradient theory predictions based on the cubic-plus-association equation of state and experimental data. These IFTs decrease with increasing pressure and temperature. The effects of pressure on these IFTs are less pronounced at high temperature. Here, the positive surface excess of N₂ explains the decreasing behavior of the IFT as a function of pressure. It can be seen that the surface excess of N₂ is reduced as the temperature is raised. This explains the less pronounced effects of the pressure on the IFTs at high temperature. The simulated water contact angle (CA) of the N₂ + water + silica system is in the range of 38.6-54.5°. An important finding is that under the studied conditions, these water CAs are not strongly influenced by temperature and pressure. Here we find that the effects of the IFT between H₂O and N₂ are more pronounced on the adhesion tensions. The IFT between silica and H₂O is found to be much lower than that between silica and N₂ under all conditions. Negligible amounts of N₂ were found to be adsorbed at the interface between the droplet and the silica surface. The relatively higher capillary pressure of the N₂ + H₂O + silica system indicates that the presence of N₂ might be useful for the storage of CO₂ in saline aquifers. © 2024 The Authors. Published by American Chemical Society.