Mixing-Induced Decreases in Critical Micelle Concentration in Aqueous Solution of Surfactants:Probing into the Mechanisms with 1H NMR Spectroscopy

Abstract

As revealed by 1H NMR experiments, the critical micelle concentration (CMC) of a surfactant in the aqueous solution decreases when a surfactant of different type is mixed in, a phenomenon that has been explained by the adsorption equilibrium theory. It has also been observed that the extents of mixing-induced reduction in CMC values differ among different surfactant types, depending on the interactions (absorption or repulsion) between the adsorbed surfactant molecules and the adsorption mono-layer. The results of 1H NMR experiments provided a clear picture for the so-called "synergistic effect", and thus might be used to guide the optimization of surfactant mixture formula to achieve desired performance.

Keywords

• nuclear magnetic resonance (NMR)
• mixed surfactants
• critical micelle concentrations (CMC)
• adsorption equilibrium
• synergistic effect