Micellization and aggregation properties of sodium perfluoropolyether carboxylate in aqueous solution

Abstract

Sodium perfluoropolyether carboxylate (PFPE-Na) was synthesized via hydrolyzing the corresponding hexafluoropropylene oxide oligomer (PFPF). The structure of PFPE-Na was characterized by FT-IR and 19F NMR. The micellization and aggregation properties of PFPE-Na surfactant in aqueous solution were studied systematically using equilibrium surface tension, electrical conductivity, dynamic surface tension, steady-state fluorescence, transmission electron microscopy (TEM) and contact angle methodologies. The results of equilibrium surface tension at 25°C showed that the critical micelle concentration (CMC) and the surface tension at CMC (γCMC) of PFPE-Na aqueous solution are lower than sodium perfluorooctanoate [NaPFO, C7F15COONa], which revealing that as a kind of environment-friendly surfactant, PFPE-Na is a perfect substitute of NaPFO. Electrical conductivity measurements implied that the micellization of PFPE-Na in aqueous solution was an exothermic and entropy-driven process in the range of temperature investigated. Steady-state fluorescence and transmission electron microscopy (TEM) may indicate that PFPE-Na self-assemble in aqueous solution to form larger spherical aggregates with the increase of concentration. In addition, dynamic surface tension measurements of PFPE-Na solution showed an extremely efficient adsorption at concentrations above CMC while the determination of contact angle of PFPE-Na showed the wetting ability was general.