Concentration dependence of the low-shear viscosity of polyelectrolyte micro-networks: From hard spheres to soft microgels

The low-shear viscosity of polyelectrolyte microgels is studied as a function of concentration, crosslink density and ionic strength. The variation of the viscosity with volume fraction is very similar to that found in hard-sphere colloidal suspensions. In salt-free dispersions, osmotic effects are responsible for the de-swelling of microgels at high polymer concentration. This "softening” effect modifies the viscosity near the overlap concentration