Interfacial properties of the aromatic hydrocarbon + water system in the presence of hydrophilic silica

Molecular dynamics simulations and density gradient theory are used to get insights into the interfacial behavior of the aromatic hydrocarbon + H2O and aromatic hydrocarbon + H2O + silica (hydrophilic) systems under geological conditions. Four aromatic hydrocarbons are considered, namely, benzene, toluene, ethylbenzene, and o-xylene. The increase in the IFT with increasing pressure for the aromatic hydrocarbon + H2O system may be explained by a negative surface excess of the aromatic hydrocarbon. These surface excesses follow the order benzene < toluene < ethylbenzene < o-xylene and are directly correlated with the aromatic-aromatic interactions. The simulated contact angles of water are in the range of about 81–93°(in many instances "degree" sign is not in the superscript) for the aromatic hydrocarbon + H2O + silica system and are almost similar for all studied aromatic hydrocarbons. Furthermore, the interfacial behavior of, for example, the aromatic hydrocarbon + H2O + silica system is compared with that of the hexane + H2O + silica system. The IFT of the hexane + H2O system is much higher than that of the aromatic hydrocarbon + H2O system. The effect of pressure on the IFT of the hexane + H2O system is much stronger than that of the aromatic hydrocarbon + H2O system. The simulated contact angle of water for the hexane + H2O + silica system is in the range of about 58–77° and is lower than that of the aromatic hydrocarbon + H2O + silica system. Interestingly, in all studied systems, thin water films are found at the silica surface in the hydrocarbon-rich region.