Measurements The surface tension of the aqueous solutions of the above mentioned surfactant mixtures was measured at 293 K by a Krüss K9 tensiometer according to the platinum ring detachment method(du Nouy’s method). Krüss K9 tensiometer was calibrated by taking the procedure of C. Huh and S.G. Mason into account [15]. The ring was cleaned with distilled water and heated to the red color with a Bunsen burner before each measurement. In all cases 10 or more successive measurements were performed. The root-mean-square deviation of our surface tension data depending on the surfactant concentration was in the range from ±0.1 to ±0.2 mN/m and the standard uncertainty (standard deviation of the mean) was in the range from ±0.025 mN/m (calculated for 16 surface tension values for each surfactant mixture concentration in the range of its low concentration) to ±0.063 mN/m (calculated for 10 surface tension values for each surfactant mixture concentration in the range of its high concentration), respectively. The temperature was controlled by a jacketed vessel joined to the thermostatic water bath with the accuracy ±0.01 K.