抄録
By means of surface tension measurement (Wilhelmy method), micellization and adsorbed film formation were investigated for three combinations of mixed surfactant systems: a typical anionic surfactant, sodium dodecylsulfate (SDS) was combined with three nonionic surfactants used as membrane-protein solubilizers, n-alkyl (octyl, nonyl and decyl)-N-methylglucamides (MEGA-8, MEGA-9 and MEGA-10, respectively) in water at 30°C. The data of surface tension (γ) versus logarithmic total molality of both single and mixed surfactant systems (mt) plots as a function of mole fraction of surfactant 2 (2 corresponds to MEGA-n’s), X2, enabled us to determine critical micellization concentration (CMC), minimum surface tension at CMC (γCMC), surface excess (Γt), mean surface area occupied by a molecule (Am) and parameters related to synergism in surface activity such as pC20 and CMC/C20. Based on the regular solution theory, the relation of compositions of the singly dispersed phase (X2) and the composition of the adsorbed film phase (Z2) were estimated, and then the interaction parameters in micelles (ωR) and in adsorbed film (ωA) were also calculated. Both the CMC-X2 and CMC-Y2 curves were found for all combinations to show a negative deviation from ideal mixing, and even the curve of mt (bulk phase concentration) versus Z2 produced a prominent negative ωA. A marked synergism in surface tension reduction was observed for these MEGA-n’s mixtures with SDS; the extent of the synergism increased in the order of MEGA-8, -9 and -10. A positive synergism was observed, even from the partial molecular area (PMA) and the minimum free energy at surface G(S)min= (γCMC·Am·L) where, L is the Avogdro’s number.
