Micellization and adsorbed film formation of a binary mixed system of anioniconionic surfactants

摘要

Micelle formation in water and adsorbed film formation at the air/water interface were investigated by surface tension measurement of a mixed surfactant system: the combination of sodium salt of alpha-sulfonatomyristic acid methyl ester (alpha-SMy.Me) with decanoyl-N-methylglucamide (MEGA-10). alpha-SMy.Me and MEGA-10 can form well-mixed micelles with the aid of a strong interaction between headgroups, and accordingly the critical micelle concentration (cmc) as a function of mole fraction of MEGA-10 in the surfactant mixture (X-MEGA10) deviates negatively from ideal mixing. The micellar phase curve (cmc-Y-MEGA10 relation) was simulated by using the interaction parameter omega(R) = -2.1; the curve indicated the existence of an azeotrope formed by a 3:2 mixture (at X-MEGA10 = Y-MEGA10 = 0.4) Further, we derived equations related to the composition in the adsorbed film (Z(i)) equilibrated with monomers in bulk solution and to the interaction parameter (W-A), and then constructed a phase diagram including two relations of cmc vs X-MEGA10 and cme vs Z(MEGA10). From the diagram an azeotrope was found to be formed by the 1:1 mixture (at X-MEGA10 = Z(MEGA10) = 0.5), suggesting that the composition in micelles (Y-i) differs from that in the adsorbed film (Z(i)). The surface tension (gamma) vs logarithmic molality (ln m) curve at every 0.1 increment in X-MEGA10 showed synergistically enhanced surface activity. From the slope of the gamma vs ln m curve just below cmc, the surface excess (Gamma) was determined and then the mean molecular area (A(m)) was calculated as a function of X-MEGA10 BY analysis of A(m) data, the partial molecular area (PMA) of each component was determined as a function of X-MEGA10; this also showed a large deviation from ideal mixing (the additivity rule). [References: 41]