Translational motion and association in aqueous sodium cholate solutions

Abstract

Self-association in aqueous sodium cholate solutions was studied at 25°C by determining the translational self-diffusion coefficients of water molecules, cholate ions, and sodium ions. Association was found to be much more gradual than for simple surfactants. Thus association starts at a concentration of about 0.014 mole/kg and progresses continuously up to the highest concentrations studied (0.5 mole/kg). The counterion association degree, which was derived from the sodium ion diffusion coefficient, is much lower than for typical micelle-forming substances. From the concentration dependence of the water self-diffusion coefficient the micellar hydration number was estimated. Hydration was found to be much more extensive than for simple surfactant micelles.