Interfacial and micellar synergistic interactions between a phosphonium surface active ionic liquid and TX-100 nonionic surfactant: Surface tension and 1H NMR investigations

Abstract

The adsorption and self-aggregation behaviors of a mixed system made of a cationic surface active ionic liquid (SAIL), dodecyltriphenylphosphnium bromide (C12TPB), and a nonionic surfactant, polyoxyethylene p-tertoctylphenyl ether (TX-100), were investigated in aqueous solution using tensiometry and 1H NMR measurements. From the surface tension data, relevant physico-chemical parameters were determined for different proportions of the components: critical micelle concentration (cmc), surface saturation adsorption, minimum surface area per surfactant molecule and surface tension at the cmc. The obtained data were treated through different theoretical models, namely those of Clint, Rubingh, Maeda and Rosen, which allow the determination of key thermodynamic properties. The results revealed, in both the mixed micelles and surface monolayer, the existence of a non-ideal behavior due to rather strong attractive links, confirmed by the 1H NMR data analysis. They are attributed mainly, besides the hydrophobic interaction, to firstly the ion–dipole interaction and the complex formation between the polyoxyethylene head of TX-100 and the quaternary phosphonium group of C12TPB, and secondly to an intermolecular π-π stacking and a hydrogen-bonds formation between the protons in α position of the phosphonium and the oxygen atoms of polyoxyethylene units of TX-100, giving rise to a strong synergism.