Molecular Dynamics Study on the Adsorption of Heavy Oil Drops on a Silica Surface with Different Hydrophobicity

Adsorption of oil droplets on different hydrophilic and hydrophobic silica surfaces was studied by molecular dynamics simulations. The surfaces included fully hydrophilic, 50% hydrophobic, and fully hydrophobic silica, and the oil droplet belongs to a heavy oil drop containing asphaltenes and resins. The simulated results showed that the oil droplet is easier to adsorb on the fully hydrophobic system, and the oil phase moves faster than that on the other silica surface. After adsorption of the oil drop finished, the asphaltene and resin molecules on different surfaces showed different aggregated structure. On the fully hydrophilic surface, the asphaltene and resin molecules aggregate through a face-to-face stacking interaction, and they adsorbed vertically on the silica surface. This is attributed to formation of hydrogen bonding between the model molecules (asphaltenes and resins) and the silica surface. This result indicates that the hydrophilic surface has a stronger interaction with the asphaltenes and resins than the other surfaces. The calculated free energy of adsorption of the model molecules on different surfaces further proves that the fully hydrophilic surface has a stronger adsorption capacity to heavy oil drop.