INTERACTION BETWEEN CATIONIC FLUOROCARBON SURFACTANT AND POLYOXYETHYLATED SURFACTANTS HAVING A SULFATE GROUP

Interaction between a cationic fluorocarbon surfactant, )(2-hydroxy-3- perfluorooctylpropyl)-methylammonium chloride (DEFUMAC) and sodium dod ecyl poly(oxyethylene)sulfate (SDE(n)S, n = 3, 5, 8) in dilute aqueous solutions has been investigated by means of surface tension, fluoresc ence 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 solutio n no crystals are formed at any molar fraction in the DEFUMAC-SDE8S sy stem, whereas precipitation of crystals is observed over wide regions in the DEFUMAC-SDE3S or SDE5S systems. On the other hand, in the dilut e solution, the mixed critical micelle concentration (CMC), the surfac e tension at the CMC, an interaction parameter beta (from regular solu tion theory), the apparent aggregation number and the diffusion coeffi cient of the mixed micelles all depend on the oxyethylene chain length of SDE(n)S. These characteristics change markedly with decreasing val ue of n. This is predominantly due to the strong electrostatic attract ive interaction between the surfactants in spite of the mutual phobici ty of hydrocarbon and fluorocarbon chains.