Rheology of starch-based colloidal microgels

Steady state rheology experiments were performed on aqueous suspensions of starch-based particles in dilute and concentrated regimes to quantify the swelling degree of the particles and to determine the zero and infinite shear viscosities, respectively. Results showed that the starch-based particles behaved like microgels (with volumes swelling at least by factor 15), and like polyelectrolytes, since in de-ionised suspensions, the reduced viscosity decreased with increasing particle concentration. Analogous results are obtained for reference charged rigid silica spheres, which approach the hard sphere limit for increasing ionic strengths. Besides changes in shape of the microgels, the expansion of the electrical double layer upon decreasing the particle concentration plays an substantial role in the anomalous viscosity behaviour. The starch-based colloidal microgels exhibit shear-thinning behaviour in aqueous suspensions. In concentrated regimes, the dependence of the zero and infinite shear viscosities on the volume fraction appears to be comparable to that of reference microgels.