Behaviour of the fluorocarbon surfactants in the monolayer at the water–air interface and in the bulk phase

The measurements of density, viscosity, conductivity, pH, surface tension and steady state fluorescence for the aqueous solutions of the fluorocarbon surfactants, Zonyl FSN-100 (FC6EO14) and Zonyl FSO-100 (FC5EO10) have been made at 293 K. On the basis of the obtained results and the literature data the activity of the surfactant at the solution–air interface, the standard Gibbs free energy of adsorption and the critical micelle concentration (CMC) were determined. It appeared that depending on the physicochemical parameter used for CMC determination, it is possible to obtain two different values of it corresponding to different sizes of the micelles, which is difficult to find in the literature. The average aggregation number calculated from the fluorescence data for FC6EO14 and FC5EO10 and their second value of CMC corresponds to the sphere with the radius equal to the average length of their molecules.