The mixed micellar size, relative arrangement and interaction sites of the nonionic sugar-based surfactant n-dodecyl-β-D-maltoside (DM) and dodecyl trimethyl ammonium chloride were studied using NMR by self-diffusion coefficient, spin-spin and spin-lattice relaxation time, and two-dimensional nuclear Overhauser enhancement (2D NOESY). Self-diffusion coefficient suggests that the size of the mixed micelles is largely dependent on the DM. The small T2/T1 values suggest tight molecular packing in the mixed micelles of DM and DTAC. 2D NOESY results reveal that the methylene group next to the ammonium head is in the near vicinity of penultimate sugar ring, and the two hydrophobic chains of DM and DTAC molecules are side by side in the interior of the micellar core. The inter-molecular interaction and distance are changed with the difference of DM/DTAC ratios. DM/DTAC ratios of 1∶4 to 1∶8 are better than other ratios for synergistic performance. The intermolecular interaction was supported by the contrary changes of spin-spin relaxation time (T2) after mixing.

Key words: n-dodecyl-β-D-maltoside, dodecyl trimethyl ammonium chloride, mixed micellar structure, intermolecular interaction site, mixing ratio, 1D and 2D 1H NMR