Enhanced oil recovery: QM/MM based descriptors for anionic surfactant salt-resistance

A major challenge in enhanced oil recovery is the salt-resistance of surfactants. Theoretical research into the salt-resistance of anionic surfactants is mainly limited to experimental results. In this paper, four virtual descriptors of two anionic surfactants were studied by molecular dynamics simulation at the atomic level and wavefunction analysis at the quantum level. The four descriptors are the number of hydrogen bonds, ion distribution, radial distribution function (RDF) and the ionic bond strength. Combining the experimental data of the interfacial tension at the critical micellar concentration and different ion concentrations, the relationships between these four descriptors and the interfacial properties of anionic surfactants were determined. The four descriptors are very accurate indicators of anionic surfactant performance evaluation, and as a result of the atomic level correlation between the descriptors and anionic surfactants, the QM/MM based descriptors could reflect the rules for different surfactants or different ion concentration gradients. The IRI method has been shown to be a general protocol in the analysis of the effect of different ions on the interfacial properties of anionic surfactants. Four virtual descriptors such as hydrogen bond, ion distribution, RDF and ionic bond strength were verified to be important evaluation parameters that could describe the salt-resistance of surfactants. Combining the experimental data of the interfacial tension at the critical micellar concentration and different ion concentrations, the relationships between these four descriptors and the interfacial properties of anionic surfactants were determined.