Mixed Micellization of Cationic Gemini Surfactants with Primary Linear Alkylamines

Due to the potential use of amines as co-surfactants in microemulsions, the effect of adding alkylamines (C-4-C8NH2) on the aggregation properties of cationic gemini surfactants [pentanediyl-1, 5-bis(dimethylcetylammonium bromide) and hexanediyl-1, 6-bis(dimethylcetylammonium bromide), referred to as 16-5-16 and 16-6-16 compounds] has been studied using tensiometry at 303 K. Data on critical micelle concentration (CMC), the surface properties C-20 (the surfactant concentration required to reduce the surface tension by 20 mN/m), Gamma(max) (maximum surface excess), Amin (minimum surface area per molecule) evaluated from the surface tension versus surfactant concentration plot, the interaction parameters beta(sigma) (for mixed monolayer formation at the aqueous solution/air interface), and beta(m) (for mixed micelle formation in aqueous medium) are reported. A synergistic interaction was observed both in the micelle as well as at interface, as evident from interaction parameters. Theoretical models of Clint, Rubingh and Rosen were used to explain and compare the results. More synergistic interaction was observed in 16-5-16 as compared to 16-6-16. The CMC values of 16-s-16 (s = 5, 6) decreased with increasing amine concentrations and the extent of the effect followed the sequence: octylamine > heptylamine > hexylamine > pentylamine > butylamine.