RHEOLOGY OF SULFONATED POLYSTYRENE SOLUTIONS

We report the apparent viscosity of aqueous solutions of a well-charac terized synthetic polyelectrolyte, the sodium salt of polystyrene sulf onate. Using two rheometers we measure the apparent viscosity over mor e than five decades of shear rate to determine the Newtonian viscosity and the onset of shear thinning, which is inversely proportional to t he relaxation time. We study five decades of polyelectrolyte concentra tion, from the dilute to the entangled regimes, and three decades of a dded salt (NaCl) concentration, on a single polyelectrolyte sample. Mu ch of the viscosity data in the literature are shown to be in the shea r thinning regime and are not indicative of the Newtonian viscosity. O ur data for viscosity and longest relaxation time are qualitatively co nsistent with a recent scaling theory. There are systematic deviations from this simple theory, including the failure of the well-establishe d Fuoss law, which is shown to be obeyed by the apparent viscosity onl y at higher shear rates.