1H NMR study of micelles formed by mixture of nonionic n-dodecyl- β- d-maltoside and cationic gemini surfactants

Abstract

The relative arrangement and interaction of the cationic butane-1,4 bis(dodecyl dimethyl ammonium chloride) gemini (12–4–12) with nonionic sugar-based surfactant n-dodecyl- β- d-maltoside (DM) was studied by NMR techniques. It is shown that the methylene group next to the ammonium head in the gemini is close to the penultimate sugar ring of DM in their mixed micelles, and the hydrophobic chain of DM molecule and the two hydrophobic chains of 12–4–12 gemini are side by side in the interior of the micellar core. The size of the mixed micelles is largely dependent on the DM composition at fixed total surfactant concentrations. At fixed DM concentration, the interaction between DM and 12–4–12 gemini increases gradually with decrease in DM/12–4–12 ratio from 1:1 to 1:4. At higher 12–4–12 gemini ratios of 1:6 and 1:8.5, the intermolecular interaction starts to decrease gradually, implying the intramolecular interaction is more dominant than intermolecular interactions in the mixed micelles. NMR results suggest that relatively strongest intermolecular interactions in the mixed micelles of DM and 12–4–12 gemini exist at DM/12–4–12 mixing ratio of 1:4.