On the interpretation of transport properties of sodium cholate and sodium deoxycholate in binary and ternary aqueous mixtures

Sodium cholate (NaC) and sodium deoxycholate (NaDC) in binary and ternary aq. mixts. were investigated by means of surface tension, ESR spectroscopy (EPR), small angle neutron scattering (SANS) and mutual diffusion coeff. anal. Concerning the NaC-H2O and NaDC-H2O binary mixts., the surface tension, EPR and diffusion measurements confirmed the formation of micelles above a well detectable crit. concn. The SANS data indicated for both systems, the formation of ellipsoidal micelles whose major axis increased with concn. and minor axis remained const. The data were interpreted under the assumption that aggregate growth occurred via hydrogen bonding of small aggregates along one preferential direction. For the NaC-NaDC-H2O ternary mixts., the surface tension and EPR results were in good agreement with the Clint model prediction for the ideal mixed micellization. Based on this model, the SANS data enabled a complete description of the mixed aggregates in terms of dimensions, compn. and concn. In turn, this strategy allowed for a satisfactory interpretation of the main and cross-term diffusion coeff. trends, which are quite complex.