Synergism in Mixed Zwitterionic Surface Activity Ionic Liquid and Anionic Surfactant Solution: Analysis of Interfacial and Micellar Behavior

Abstract

Synergistic interactions between zwitterionic surface active ionic liquids (SAILs), N-alkyl-N′-carboxymethyl imidazoliumm inner salts ([N-C n , N′-CO2-Im], n = 12, 14), and a traditional twin-tail anionic surfactant (dioctyl sulphosuccinate sodium salt, AOT) in aqueous solution has been studied by surface tension and fluorescence measurements at 298.15 K. The results imply that the mixed systems have superior surface activity in comparison to individual surfactant, and they all present a non-ideal behavior with synergism. The strength of interactions between two surfactants increases with the enhancement of the hydrocarbon chain of the zwitterionic SAILs. Compared with interaction parameters in mixed monolayer, the larger value of interaction parameters in mixed micelles indicates that the mixed micelle formation is more favorable. Additionally, a series of thermodynamic parameters such as the standard Gibbs free energy of adsorption (), the standard Gibbs free energy of micellization (), and excess free energy of micellization (ΔG ex) have been calculated. The negative values of and show that both micellization and adsorption of surfactants are spontaneous, while the negative value of ΔG ex indicates the formation of stable mixed micelles for [N-C n , N′-CO2-Im]/AOT mixture, which can potentially be useful for industrial preparations and medicinal formulations.