Effect of nano-SiO2 and surfactants on the oil-water interfacial properties

This study aimed to clarify the effects of different types of nano-SiO2 and surfactants on the oil-water IFT and IFR. These interfacial properties were demonstrated to be influenced by the interaction between the surfactant, the nano-SiO2 and the oil component. The interaction between nano-SiO2 and oil components and their adsorption at the crude oil-water interface were closely related to the pH values, which, on one hand, determined the amount of charge and the amount of hydroxyl groups on the surface of SiO2, and on the other hand affected the chargeability of some polar components in the crude oil. Surfactants were observed to compete with other components at the oil-water interface for absorption. When the surfactant concentration was high, the surfactant could replace the colloid and asphaltene at the oil-water interface, and the adsorption of SiO2 and crude oil components at the oil-water interface was inhibited, which resulted in a relatively low interfacial modulus. The electrostatic interaction between nano-SiO2 and cationic surfactant and that between nano-SiO2 and protonated nonionic surfactant could contribute to the formation of composite films at the interface, and thus higher interfacial dilatational modulus, whereas the mutual electrostatic repulsion between nano-SiO2 and the anionic surfactant would promote one of the two to move towards the interface. Therefore, it could be inferred that different oil-water systems with different interfacial properties could be constructed by adjusting the pH value of the nano-SiO2 solution, the surfactant type, the molar ratio of the surfactant to the nano-SiO2, and the oil phase composition.