Extended Investigation of the Aqueous Self-Assembling Behavior of a Newly Designed Fluorinated Surfactant

Abstract

The physicochemical behavior of the newly synthesized fluorinated 5-hydroxyamino-3-perfluoroheptyl-1,2,4-oxadiazin-6-one (PFHO) surfactant was investigated. Thermal analysis showed that the pure surfactant is thermally stable under an inert atmosphere to 135 degrees C, which is several degrees higher than the melting point (99 degrees C). PFHO is rather active at the water/air interface where it assumes a standing up configuration. It exhibits an enhanced self-assembling behavior; accordingly, the critical micellar concentrations at some temperatures are 2 orders of magnitude lower than those of a similar surfactant having the same phobicity, such as sodium perfluorooctanoate. Even in the dilute domains, PFHO forms large micelles, detected by dynamic light scattering studies, that are precursors of the gel occurring at rather low composition (only 2.0% w/w at 25 degrees C). Optical microscopy evidenced cylindrical aggregates in gel systems whereas differential scanning calorimetry and viscosity showed that the gels are stable over a wide temperature range to ca. 70 degrees C where they undergo a reversible gel --> fluid transition. Finally, percolation theory combined with data provided by the experimental studies enabled us to predict the PFHO gelation process correctly, in very good agreement with the experimental findings.