Effect of polymer-surfactant structure on its solution viscosity

Polymer-surfactant interactions in solutions are important in wide range of applications. The interactions lead to the formation of various polymer-surfactant structures. The solution viscosity is dependent on the structure. Here we have studied the dependence of viscosity and structure on the composition of polymer-surfactant mixture. We have used non-ionic polymer polyvinyl pyrrolidone (PVP) and negatively charged surfactant sodium dodecyl sulfate (SDS). PVP behaves as a negatively charged polyelectrolyte in pure water at pH 7.4. It interacts with SDS through hydrophobic interaction. This leads to the polymer saturation point (PSP). PVP behaves as a positively charged polyelectrolyte at pH 2.4. The SDS neutralizes the opposite charge of polymer. After the neutralization point of PVP, excess SDS interacts with the polymer through hydrophobic interaction. From the data of charge neutralization, charge on the polymer is calculated. From the data of PSP on PVP at various concentrations, we calculated the number of SDS molecules per PVP molecule. The structure of PVP-SDS complexes is observed by using transmission electron microscope at room temperature. The viscosity data are explained from the observed structure of PVP-SDS mixture. (C) 2010 Curtin University of Technology and John Wiley & Sons, Ltd.