Interfacial properties of the hexane + carbon dioxide + water system in the presence of hydrophilic silica.

Molecular dynamics simulations were conducted to study the interfacial behavior of the CO 2 + H 2 O and hexane + CO 2 + H 2 O systems in the presence of hydrophilic silica at geological conditions. Simulation results for the CO 2 + H 2 O and hexane + CO 2 + H 2 O systems are in reasonable agreement with the theoretical predictions based on the density functional theory. In general, the interfacial tension (IFT) of the CO 2 + H 2 O system exponentially (linearly) decreased with increasing pressure (temperature). The IFTs of the hexane + CO 2 + H 2 O (two-phase) system decreased with the increasing mole fraction of CO 2 in the hexane/CO 2 -rich phase x CO 2 . Here, the negative surface excesses of hexane lead to a general increase in the IFTs with increasing pressure. The effect of pressure on these IFTs decreased with increasing x CO 2 due to the positive surface excesses of carbon dioxide. The simulated water contact angles of the CO 2 + H 2 O + silica system fall in the range from 43.8° to 76.0°, which is in reasonable agreement with the experimental results. These contact angles increased with pressure and decreased with temperature. Here, the adhesion tensions are influenced by the variations in fluid-fluid IFT and contact angle. The simulated water contact angles of the hexane + H 2 O + silica system fall in the range from 58.0° to 77.0° and are not much affected by the addition of CO 2 . These contact angles increased with pressure, and the pressure effect was less pronounced at lower temperatures. Here, the adhesion tensions are mostly influenced by variations in the fluid-fluid IFTs. In all studied cases, CO 2 molecules could penetrate into the interfacial region between the water droplet and the silica surface.