Micellization of mixed system of bile salt and nonionic surfactant: Sodiumdeoxycholate and decanoyl-N-methylglucamide

Micelle formation was studied for mixed surfactant systems of a nonionic su rfactant, nonanoyl-N-methylglucamine (MEGA-10) with a bile salt, sodium deo xycholate (NaDC), in water at 30 degrees C. NaDC and MEGA-10 are quite diff erent from each other in terms not only of hydrophobic but also of hydrophi lic groups. Surface tension of the aqueous solution (gamma) at different mi xing ratios was measured by the drop volume method, and critical micellizat ion concentrations (CMCs) were determined from the gamma vs CMC curves at d iscrete mole fractions of MEGA-10 (X-MEGA) in the surfactant mixture. The C MC-X,,, curve showed a positive deviation from ideal mixing, The apparent i nteraction parameter (W-R) upon micelle formation was evaluated by applying the Rubingh equations derived on the basis of the regular solution theory. The different theory developed by Motomura et al, has been also applied. T he analysis of CMC data indicated that the properties of mixed micelles are different between the ranges below and above X-MEGA congruent to 0.2 where an azeotrope exists and that the composition of mixed micelles is very sim ilar to that of monomeric species in bulk solution. (C) 1998 Academic Press .