The Effects of Dynamic Noncovalent Interaction between Surfactants and Additional Salt on the pH‐Switchable Interfacial Tension Variations.

The dynamic noncovalent interaction between the anionic surfactant sodium dodecyl benzene sulfonate (SDBS) and 1,3‐diphenylguanidine (DPG) was employed to control the interfacial activity of the surfactant. At high HCl concentration (1000 mg L−1), the SDBS/DPGn+ system could reduce the water/oil interfacial tension (IFT) to 10−4 mN m−1 order of magnitude, which was much lower than the IFT values in the SDBS/DPG+ system with a low HCl concentration (100 mg L−1) and the individual SDBS system by three and four orders of magnitude, respectively. The pH‐switchable protonation of amido groups in DPG molecules determines the SDBS/DPG molecular interaction and the amplitude of IFT reduction, which was confirmed by control experiments using two other surfactants (sodium dodecyl sulfate [SDS] and dodecyl trimethylammonium bromide [DTAB]). Moreover, the investigation of the NaCl and temperature effects on the IFT indicated the intensity of mixed SDBS/DPGn+ adsorption layers at the water/oil interface. [ABSTRACT FROM AUTHOR]