Surface Tension, Viscosity, and Refractive Index of Sodium Dodecyl Sulfate (SDS) in Aqueous Solution Containing Poly(ethylene glycol) (PEG), Poly(vinyl pyrrolidone) (PVP), and Their Blends

Taking into consideration the importance of the polymer–surfactant system, in present manuscript we discuss the intermolecular interactions present in solution containing sodium dodecyl sulfate (SDS) in six different solvent concentrations of polymer and their mixtures in their mass ratio [1 g of PEG (m₁), 0.8:0.2 PEG/PVP (m₂), 0.6:0.4 PEG/PVP (m₃), 0.4:0.6 PEG/PVP (m₄), 0.2:0.8 PEG/PVP (m₅), and 1 g of PVP (m₆) in 100 mL of distilled water] having a molal concentration corresponding to 1.66 mmol·kg^–1, 1.38 mmol·kg^–1, 1.10 mmol·kg^–1, 0.81 mmol·kg^–1, 0.53 mmol·kg^–1, and 0.25 mmol·kg^–1, respectively. It suffices to mention here that the concentration (molality) corresponds to the total polymer content in the solution. All of the measurements were carried out at three different temperatures, that is, 293.15, 303.15, and 313.15 K. The whole experiment was carried out with techniques like surface tension, viscosity, and refractive index measurements. Different parameters of relevance like surface excess (Γ_max), minimum area per molecule at air–water interface (A_min), relative viscosity (η_r), viscous relaxation time (τ), and limiting dielectric constant (ε_∞), and so forth have been evaluated from surface tension, viscosity, and refractive index measurements. This persistence of the surface tension (γ) beyond the critical micelle concentration (CMC) appears to suggest that the aggregate formation in the presence of the PEG or PVP or their blends is sufficiently large. The close approximated value of relative viscosity to the unity implies that the conformational changes in the polymer are minimal. The refractive index measurements further reveal that the overall polarizability of the studied systems increases with an increase in the amount of polymer in the solution.