Ionic surfactant–polymer interaction in aqueous solution

The interactions in aqueous solution between poly(vinylpyrrolidone) (PVP) and sodium nonanoate (C8COONa), sodium octylsulfonate (C8SNa), lithium perfluorononanoate (C8FCOOLi), respectively, were investigated. In all the studied systems, the presence of PVP induces a lowering of the aggregation number of the surfactant as evidenced by fluorescence quenching measurements. However, no direct surfactant–polymer interaction has been found for the systems C8COONa–PVP and C8SNa–PVP. Strong hydrophobic interaction in the system C8FCOOLi–PVP has been shown by the fluorescent behavior of pyrene used as a probe. The presence of the fluorinated surfactant induces an increment of ∼14% of the polymer gyration radius, as shown by viscosimetry. Calorimetry confirms the experimental results obtained through fluorescence and shows that the adsorption of C8FCOOLi on PVP is an endothermic process.