Aggregation and Adsorption Behaviors of Sodium Deoxycholate in Water-Ethylene Glycol Medium

Critical micelle concentrations (cows) of sodium deoxycholate (SDC) were determined at 25 C in water + ethylene glycol (EG) medium (mass fraction of EG, w(EG) x 10(2) = 0, 10, 20, 30, 40, 50, and 60) by measuring surface tension, fluorescence emission intensities of pyrene probe, and conductance. Cmc was also determined in the presence of NaCl from the surface tension isotherms, and counter ion binding constants (beta) of SDC were evaluated by applying the Corrin-Harkins equation and slope-ratio method. The value of beta in water is about 0.18 and becomes almost half of this value in water + EG. Surface excess at the cmc decreases as the EG amount increases, but increases on adding NaCl. Gordon parameter and ratio of surface tension of the medium to that of the surfactant solution at the cmc are used to represent solvophobicity.