A molecular simulation study of ethoxylated surfactant effects on bulk and water/crude-oil interfacial asphaltenes

Oil/water interfacial properties play a crucial role in the chemical industry, especially in enhanced oil recovery (EOR) and emulsion behavior. Among the oil components, asphaltenes can form aggregates and increase the rigidity of the interfacial film, and this can enhance the stability of the emulsions. Here, all-atom molecular dynamics simulations are used to evaluate the molecular-level behavior of two ethoxylated surfactants in water/ oil/asphaltene systems, where the oil phase is modeled as a realistic mixture of n-alkanes, cycloalkanes, and aromatic molecules. The addition of the evaluated surfactants considerably reduces the ordering of the asphaltene molecules in the bulk oil phase. In the oil/water systems, the interfacial region selectively absorbs the surfactant molecules, and there is a slight difference in the interfacial behavior of different asphaltene molecules, mostly originating from their molecular structure. The presence of the ethoxylated surfactant molecules considerably affects the interfacial ordering of the asphaltene molecule in the interfacial region, and free energy calculations indicate that the sorbitan-based surfactants result in a larger increase in the interfacial sorption of the studied asphaltenes.