Adjustable surface activity and wetting ability of anionic hydrocarbon and nonionic short-chain fluorocarbon surfactant mixtures: Effects of Li+ and Mg2+

Abstract

Achieving wide variation ranges and various adjusting modes of the performances for surfactant mixtures is still a significant challenge which limits the extensive application of surfactant mixtures. Herein, we reported the physicochemical properties and performances of hydrocarbon/fluorocarbon surfactant mixtures constituted with an anionic hydrocarbon surfactant, sodium dodecyl sulfate (SDS), and a tri-block nonionic short-chain fluorocarbon surfactant (F9EG13F9). Meanwhile, the effects of Li+ and Mg2+ on them were investigated. The surface tension and contact angle measurements were adopted to reflect the surface activity and wetting ability of SDS/F9EG13F9 mixtures. The data showed that the surface tensions at the critical micelle concentrations and the contact angles on polytetrafluoroethylene film of these surfactant mixtures are 33.5–21.4 mN/m and 118.0–58.7°, respectively, which indicates that their surface activity and wetting ability possess wide variation ranges. Furthermore, the micellization, adsorption and thermodynamics behaviors of mixed surfactants were also analyzed using a series of theoretical parameters based on the regular solution theory, Clint’s model, Maeda’s model, etc. The results approved that Li+ and Mg2+ immensely reduce the electrostatic repulsion effect of SDS and increase the adsorption of SDS at phase interfaces to enhance mixed monolayer packing, in which the effect of Mg2+ is stronger than that of Li+. Thus, precisely adjustable surface activity and wetting ability can be realized by changing the molar ratio and adding the different cations, which enables SDS/F9EG13F9 mixtures to possess tunable performances to meet various practical application requirements.