Self-aggregation of surfactants in water solution by NMR

Dynamic behavior of surfactant molecules, sodium dodecyl sulfonate (SDSN), cetyl trimethyl ammonium bromide (CTAB) and triton X-100, and their micelle s in water solution at various concentrations were studied by chemical shif t, self diffusion coefficient (D) and nuclear magnetic resonance relaxation (T-1 and T-2) measurements. Experimental results show that there exist tur ning points at surfactant concentration (C) nearby the critical micelle con centration (cmc) for all of the above-mentioned parameters, which approach the constant values when C equals 5 to 10 times cmc. T-1 and T-1 measuremen ts show that when C< cmc, Triton X-100 molecules exhibit fast isotropic mot ion in water solution. After micellization, the motion of hydrophobic chain s is far away from the extreme narrowing condition, however, the long hydro philic oxyethylene chains move relatively freely, although their T-1 and T- 2 become shorter in comparison with those of the molecules in mono-molecula r state. The behavior of the hydrophobic chains within the micellar core of SDSN and CTAB is similar to that of Triton X-100 to some extent.