Influence of the polymer molecular weight on the surfactant-polymer interactions: LiPFN-PVP and SDS-PVP systems

Surface tension, viscosity, density, and 1H-NMR measurements on lithium heptadecafluorononanoate (LiPFN) aqueous solutions containing 1% poly(vinylpyrrolidone) (PVP) at different molecular weights have been carried out. The results show the influence of the polymer molecular weight on the polymersurfactant interaction and give information on the complex kinetic mechanism of the absorption of surfactant on polymer occurring through several steps. In particular the data show that, at low LiPFN concentration, the surfactant undergoes a phase transition from the molecular to the self-aggregated state. Such a kinetic step is not accompanied by conformational changes of the polymer. Increasing the LiPFN concentration causes interactions between the fluorinated micelles and the polymer to occur. The micellepolymer interactions involve selected regions of the polymer and thereafter the whole macromolecule. In such a process the PVP chains reorganize themselves around the LiPFN micelles to give dressed micelles. Surface tension measurements on sodium dodecyl sulfate (SDS) in PVP K30-water mixtures have also been carried out. Comparison of these data with those previously obtained on SDS-water-PVP K90 shows that the influence of polymer molecular weight on the polymer-surfactant interaction is not peculiar to perfluorinated surfactants.