Interaction between cationic fluorocarbon surfactant and polyoxyethylated surfactants having a sulfate group

Abstract

Interaction between a cationic fluorocarbon surfactant, bis(2-hydroxyethyl)(2-hydroxy-3-perfluorooctylpropyl)-methylammonium chloride (DEFUMAC) and sodium dodecyl poly(oxyethylene)sulfate (SDE n S, n = 3, 5, 8) in dilute aqueous solutions has been investigated by means of surface tension, fluorescence probing, solubilization, and static and dynamic light scattering measurements. The same systems in concentrated aqueous solutions have been characterized from the phase diagram. In the concentrated solution no crystals are formed at any molar fraction in the DEFUMAC-SDE 8S system, whereas precipitation of crystals is observed over wide regions in the DEFUMAC-SDE 3S or SDE 5S systems. On the other hand, in the dilute solution, the mixed critical micelle concentration (CMC), the surface tension at the CMC, an interaction parameter β (from regular solution theory), the apparent aggregation number and the diffusion coefficient of the mixed micelles all depend on the oxyethylene chain length of SDE n S. These characteristics change markedly with decreasing value of n. This is predominantly due to the strong electrostatic attractive interaction between the surfactants in spite of the mutual phobicity of hydrocarbon and fluorocarbon chains.