MIXED MICELLES OF SDS AND SODIUM CHOLATE. A NUCLEAR MAGNETIC RESONANCE DIFFUSION AND RELAXATION STUDY

A nuclear magnetic resonance diffusion and relaxation investigation, of the mixed micellar system sodium dodecylsulfate (SDS)/sodium cholate (SC) is presented. The concentration of SDS is kept constant at 15 mM and the concentration of SC is varied up to a total SC concentration of 100 mM. The diffusion coefficients of SDS and SC and the 2H elaxation rates of specifically 2H labeled SDS are measured. These quantities are used in the description of the distribution of the two surfactants in the various environments (as monomers in solution and associated into micelles). A theoretical framework based on the Bragg-Williams model is used to qualitatively describe the data. A value of the interaction parameter of SC and SDS in the micelles of X = -2 is derived form the data. The results are discussed with special reference to the use of the mixed micellar system in micellar electrokinetic capillary chromatography (MECC).