ASSOCIATION OF NONIONIC POLYMER WITH HYDROCARBON FLUOROCARBON SURFACTANT IN AQUEOUS-SOLUTION

The interaction between a nonionic polymer and a hydrocarbon or fluorocarbon surfactant has been investigated by means of surface tension, viscosity, electroconductivity, fluorescence probing, solubilization of a water-insoluble dye, and electron spin resonance (ESR). The systems studied consisted of polyvinylpyrrolidone (PVP) with lithium dodecyl sulfate (LiDS) or lithium perfluorooctane sulfonate (LiFOS). Surface tension measurements indicated that formation of PVP-surfactant complex is more favorable in the PVP-LiFOS system than in the PVP-LiDS system, and that the adsorbed amount of LiFOS is less than that of LiDS, although the CMCs of the surfactants are almost the same. In the PVP-LiFOS system, the relative viscosity and the solubilized amount of a water-insoluble dye showed a maximum at a certain concentration of LiFOS in the region between two transitions observed in the surface tension, where also a change in the slope of the electroconductivity is observed. These results indicate that shielding of effective charge of the PVP-LiFOS complex causes a conformational change of PVP wrapped around the aggregate of LiFOS with an increase of free surfactant in the bulk phase. The conformational change can be correlated with microenvironmental properties of PVP-surfactant complexes. The microviscosity estimated with ESR indicated that the head-groups of LiFOS adsorbed on PVP are less tightly packed than those of LiFOS micelles, while an opposite result was obtained in the PVP-LiDS system. In particular, the marked high viscosity at a low concentration of LiFOS in the PVP-LiFOS system can probably be attributed to rigidity of the fluorocarbon chain of LiFOS.