LAUSR

Abstract The micellization behavior of N-Lauryl sarcosine sodium (NLS, an anionic surfactant) and Dodecyltrimethylammonium bromide (DOTAB, a cationic surfactant) in aqueous solution is investigated by UV–vis spectrophotometric and conductometric methods at 298.15 K. A critical micelle concentration (CMC) were obtained for pure NLS and DOTAB as well as mixed micelles [NLS(1) + DOTAB(2)]. The CMC values of the studied system at different mole fractions (yi) are much less than that of individual surfactants (due to the strong electrostatic attraction between components after mixing). In this work, the tautomers of 1-phenyl-1, 3-butadione (or benzoylacetone) were used to obtain the mixed CMC of anionic surfactant systems by UV–Vis technique. The deviations of critical micelle concentration (CMC) from the ideal values show the interaction between NLS and DOTAB. The micellar mole fraction values (X1m and X2m) according to Rubingh approach were calculated and the results obtained reveal the same composition in the mixed micellization at most mole fraction(y1) even when the initial mixing ratio is far from equimolar. The activity coefficients of components were less than unity (f1m