Viscosity of dilute polyelectrolyte solutions

We have developed an apparatus which enables us to perform accurate measurements of the shear viscosity of low ionic strength, dilute polyelectrolyte solutions, down to polymer concentrations below one part per million. We have shown that a theoretical expression for the viscosity of such solutions can be derived using the mode-mode coupling approximation to the hydrodynamics of charged Brownian spheres. Very good agreement between the predicted and observed polymer and salt concentration and molecular weight dependence of the viscosity is observed in the low-added salt, dilute solution range. Furthermore, it appears that the theory gives a qualitatively correct description of the viscosity of semidilute solutions, indicating that independent of polyion concentration, the hydrodynamics of low ionic strength polyelectrolyte solutions is dominated by electrostatic repulsion between polyions.