The improvement of the cationic/anionic surfactant interfacial activity via the selective host-guest recognition.

Abstract Supramolecular chemistry proposed a controllable and convenient approach to construct the desired complexes used in various fields, including chemical enhanced oil recovery. β‑cyclodextrin (β-CD) can effectively enclose the surfactants to fabricate the stable inclusion complexes via the host-guest recognition. In the present report, the β‑CD effects on the interfacial activities of the mixed surfactant system consisting of N ‑dodecyl‑ N ‑methylpyrrolidinium bromide (L12) and sodium dodecyl sulfate (SDS) were systematically evaluated. Interestingly, the additional β-CD molecules greatly reduced the interfacial tension (IFT) between the L12/SDS aqueous solution and model oil (toluene and n-decane, v/v = 1:1). Due to the electrostatic attraction of L12/SDS, the β-CD molecules could selectively enclose the majority surfactants to improve the intensive arrangements of mixed surfactants at the interface. In general, the host-guest recognition facilitates the fabrications of β-CD/surfactant inclusions and decrease surfactant interfacial concentrations. The competition between the host-guest recognition and the electrostatic attraction dominates the IFT variations. Then we changed the molar ratio of L12/SDS, the dissolved order of chemicals and explored the variations of the mixed surfactants hydrophile-lipophile balance to further confirm the proposed mechanism. Moreover, the salinity and temperature effects on the IFT were systematically investigated. Graphical abstract Unlabelled Image Highlights • The additional β-CD could further reduce the IFT in mixed surfactant system. • β-CD selectively encloses the majority component in mixed surfactants at interface. • The selective host-guest recognition improves the arrangements of mixed surfactants. • The competition of host-guest recognition/electrostatic attraction determines the IFT. [ABSTRACT FROM AUTHOR]