Insights into the Assembly of the Pseudogemini Surfactant at the Oil/Water Interface: A Molecular Simulation Study

The interfacial assembly process and configuration of the pseudogemini surfactant fabricated by sodium dodecyl benzene sulfonate (SDBS) and 4,4'-oxydianilinium chloride (ODC) were studied using quantum mechanical calculations and molecular dynamics (MD) simulations. The MD simulation results revealed that SDBS and ODC showed the vertical and horizontal arrangements at the oil/water interface, respectively, and the interfacial assembled configuration presented an unexpected "H" shape rather than the traditional "U" shape. The radial distribution functions between the head groups and water molecules were employed to explore the effects of the surrounding water molecules on the SDBS/ODC interaction. Furthermore, the results of the nonbonded interaction calculations and the reduced density gradient method directly confirmed that the cation-π interaction should be responsible for the SDBS/ODC assembly mechanism and the final configuration at the oil/water interface.

pH-Switchable IFT variations and emulsions based on the dynamic noncovalent surfactant/salt assembly at the water/oil interface

Additional HCl can facilely control the dynamic noncovalent interaction between anionic surfactant sodium dodecyl benzene sulfonate (SDBS) and additional organic matter, 4,4'-oxydianiline (ODA), at the water/oil interface. At low HCl concentration (ODA/HCl molar ratio (r) = 1 : 1.5, [ODA] = 250 mg L-1), the ODA+ ions effectively enhanced the SDBS ability to reduce the water/oil interfacial tension (IFT) by about two orders of magnitude, while the (SDBS)2/ODA2+ gemini-like surfactants could be constructed at a relatively high HCl concentration (r = 1 : 4, [ODA] = 250 mg L-1), which could largely reduce the IFT to 1.19 × 10-3 mN m-1. Molecular simulation was employed to explore the interfacial activity of ODAn+ (ODA+/ODA2+) ions and the SDBS/ODAn+ interaction. The control experiments used another three surfactants to verify the proposed model. The pH-switchable gradual protonation of amino groups in ODA molecules determined the SDBS/ODA interfacial assembly, which was responsible for the reversal of IFT variations and the related emulsion behaviors.

A novel binary flooding system of a biobased surfactant and hydrophobically associating polymer with ultralow interfacial tensions

A novel alkali free binary flooding system of a biobased zwitterionic surfactant and hydrophobically associating polymer with ultralow interfacial tension at a low surfactant dosage was studied in this paper.