Rheological Properties of Mixtures of Oppositely Charged Polyelectrolytes. A Study of the Interactions between a Cationic Cellulose Ether and a Hydrophobically Modified Poly[sodium 2-(acrylamido)-2-methylpropanesulfonate

Abstract

Mixed solutions of a cationic cellulose ether (JR400) and, either poly[sodium 2-(acrylamido)-2-methylpropanesulfonate] (PAMPS), or a copolymer of sodium 2-(acrylamido)-2-methylpropanesulfonate and N-n-dodecylmethacrylamide (PAMPS-Dod) in the semi-dilute regime (10 g L-1) have been examined by oscillatory shear and steady shear measurements. Mixtures consisting of the polycation as major component and PAMPS-Dod as minor component, were viscous fluids at low polyanion concentration and became gel-like fluids with increasing polyanion content. The zero shear viscosity was a strong function of polyanion content, increasing significantly with polyanion content. The fluids are viscoelastic, exhibit Newtonian behavior at sufficiently low shear rates and become shear thinning at higher shear rates. Steady shear viscosities were fitted with the Carreau–Yasuda model yielding the time constant associated with the relaxation process. The rheological parameters concurred in support of an association model involving the formation of a crosslinked network between two oppositely charged polyelectrolytes differing greatly in molecular architecture, charge density, and conformation.