Effect of polymer conformation on polymer-surfactant interaction in salt-free water

The aim of the present paper was to study the interaction between polyvinylpyrrolidone (PVP) and sodium bis(2-ethylhexyl) sulfoccinate (AOT), as an anionic surfactant, over a temperature range of 25–60 °C by viscosity and electrical conductivity measurements. A coil-to-globule transition of PVP in water was observed. The critical micellar concentration (CMC) was determined by conductivity at 25 and 50 °C. The formation of the complex PVP-AOT in water was studied by conductivity and viscometry at 25 and 50 °C, where the polymer chain adopts respectively coil and globule conformations, and the obtained curves show two break points corresponding to the critical aggregation concentration (CAC) and the polymer saturation point (PSP). The viscometric behavior of PVP-AOT system was studied by using three selected AOT concentrations: C_AOT,1, C_AOT,2, and C_AOT,3 with C_AOT,1 < CAC < C_AOT,2 < PSP < C_AOT,3. For C_AOT,1, the system behaves as a neutral polymer. A pseudo-polyelectrolyte behavior was observed for the surfactant concentration (C_AOT,2). Above the PSP, and for the C_AOT,3 concentration, a screening effect appears due to the increase of the free AOT micelles concentrations. In presence of surfactants, the polymer chains swell especially when the PVP is in globular state.