NMR Study of the Dynamics of Cationic Gemini Surfactant 14−2−14 in Mixed Solutions with Conventional Surfactants

Three kinds of conventional surfactants, namely, two nonionic surfactants [polyethylene glycol (23) lauryl ether (Brij-35) and Triton X-100 (TX-100)], one cationic surfactant [n-tetradecyltrimethyl ammonium bromide (TTAB)], and an anionic surfactant [sodium n-dodecyl sulfate (SDS)}, were mixed into the quaternary ammonium gemini surfactant [C14H29N+(CH3)2]2(CH2)2·2Br− (14−2−14) in aqueous solution. The exchange rate constants between 14−2−14 molecules in the mixed micelles and those in the bulk solution were detected using two nuclear magnetic resonance (NMR) methods: one-dimensional (1D) line shape analysis and two-dimensional (2D) exchange spectroscopy (EXSY). The results obtained from these two methods were consistent. Both showed that mixing a nonionic conventional surfactant, either Brij-35 or TX-100, enhanced the exchange process between the 14−2−14 molecules in the mixed micelles and those in the bulk solution. In contrast, the anionic surfactant SDS and the cationic surfactant TTAB slowed the process slightly.