Micelle and solvent relaxation in aqueous sodium dodecylsulfate solutions

Abstract

Dielec. spectra were measured for aq. Na dodecylsulfate (SDS) solns. up to 0.1 molL-1 at 25° over the frequency range 0.005 ≤ ν GHz-1 ≤ 89. The spectra exhibit 2 relaxation processes at ∼0.03 GHz and 0.2 GHz assocd. with the presence of micelles in addn. to the dominant solvent relaxation process at ∼18 GHz and a small contribution at ∼1.8 GHz due to H2O mols. hydrating the micelles. Detailed anal. reveals that the micelles bind 20 H2O mols. per SDS unit, but not as strongly as trimethylalkylammonium halide surfactants do. The relaxation times and amplitudes of both micelle relaxation processes can be simultaneously analyzed with the theory of Grosse, yielding the effective vol. of a SDS unit in the micelle and the lateral diffusion coeff. of the bound counterions. The findings of this study fully corroborate recent mol. dynamics simulations on structure and dynamics of SDS micelles.