Proton NMR investigations on lithium heptadecafluorononanoate, LiPFN, in poly(vinylpyrrolidone), PVP, aqueous solutions have been carried out. NMR spectra reveal that the amphiphile, in its micellar form, links to the polymer chains by hydrophobic interactions with the pyrrolidone functional group of the polymer, causing a significant change in the PVP structure. Surface tension, viscosity, and volume measurements on LiPFN-PVP-water systems support the NMR evidence.

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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 polymer−surfactant 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 micelle−polymer 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.

Mixtures containing water, lysozyme (LYS), and a fluorinated surfactant (LiPFN) have been investigated in a wide range of protein-to-surfactant ratios. Depending on composition, sample consistency and coexistence of the different phases, different experimental methods were used. Volumetric, viscometric, surface tension, potentiometric (by a home-built ion-selective electrode), turbidity, optical polarizing microscopy, and 19F NMR experiments were used. The results obtained from the above methods have been interpreted in terms of a combination of electrostatic and hydrophobic contributions to the stability of the different phases formed in the water−LYS−LiPFN system. Solutions, gel phases, and precipitates have been observed in the range investigated in more detail. Multiphase regions have also been observed. Such rich polymorphic behavior implies the existence of interactions between the protein and surfactant. The gel phase is presumably formed by interconnections between micelles and protein-surfactant complexes, held together by protein-bound micelles and forming, presumably, interconnected necklace structures. The overlapping of different protein-surfactant aggregates to form gels requires a significant amount of time. Its formation obeys a volume fraction statistics; the width of the gel phase, in fact, is controlled by the amount of protein−surfactant complex.

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