Dilute-semidilute regime crossover in aqueous solutions of poly(acrylic acid)-sodium poly(styrene sulfonate) mixtures

Overlap and entanglement formation in aqueous solutions of mixtures of poly(acrylic acid) (PAA) and sodium poly(styrene sulfonate) (PSS) have been studied by means of light scattering and viscometry in comparison with concentration transitions in solutions of the individual polyelectrolytes. In the presence of 0.1M HCl, PAA forms a complex with PSS due to ion-dipole interactions of carboxylic groups with polyanion sulfonic groups. In the overlap region, a single diffusion mode is split into fast and slow modes, with the average scattering intensity passing through a maximum. In the region of entanglement network formation, the third mode appears, which we interpret as an interaction mode. The concentration dependences of diffusion coefficients and viscosity of the considered systems coincide with the theoretical predictions of the scaling model of polyelectrolyte solutions. In semidilute regime, the viscosity of the complex significantly exceeds that of initial components, indicating strong structuring of the solution.