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.