Abstract
The micellar properties of aqueous binary mixed solutions for two systems consisting of sodium cholate (NaC) -octaoxyethylene glycol mono n-decyl ether (C10E8) and sodium deoxycholate (NaDC) -C10E8 were studied by examining surface tension, polarity of the micelle interior and mean aggregation number determined from on pyrene fluorescence in the mixed micelles. By two theories based on the regular solution and on the excess thermodynamic quantities, the mole fraction of the bile salt in the mixed micelles near the critical micellar concentration (cmc) was found to be less than that in an aqueous mixed solution. The hydrophobicity of the interior of the mixed micelles increased with the mole fractions of bile salts in the mixed solution, particularly so for a mole fraction of 0. 57 for the NaDC-C10E8 system and 0. 75 for the NaC-C10E8 system. The mixed micelles may thus possibly change from C10E8-rich micelles to bile salt-rich micelles, particularly so for the NaDC-C10E8 system due to the stronger hydrophobicity of NaDC molecules. The aggregation number decreased with increase in the mole fractions of bile salts, approaching that of a single system of bile salts.
