Dynamics of Mixed Surfactants in Aqueous Solutions

The dynamics of mixed surfactants in aqueous solution has been studied at a molecular level by nuclear magnetic resonance (NMR) spectroscopy. The line widths and line shapes of the resonance peaks of two types of binary mixed surfactant systenns, ionic/nonionic mixed solutions (12-2-12/TX-100, 14-2-14/TX-100, 14-2-14/Brij-35, and SDS/TX-100) and ionic/ionic mixed solutions (12-2-12/TTAB and 14-2-14/TTAB), in the H-1 NMR spectra offered semiquantitative results about the influence of mixing on the surfactant exchange dynamics between monomers in aqueous solution and those in the micelles. The results showed that the exchange rates of tie mixed surfactants were enhanced by each other for the three cationic/nonionic mixed solutions, while the exchange rates were lowered by each other for the two cationic/cationic mixed solutions. As for SDS/TX-100 mixed systems, the addition of SDS made the exchange rate of TX-100 in solution faster, while TX-100 made the exchange rate of SDS slower. These results provide some information about surfactant interaction in mixed solutions.