EXPERIMENTAL STUDIES ON THE RHEOLOGY OF HARD-SPHERE SUSPENSIONS NEAR THE GLASS-TRANSITION

We have investigated the rheological behavior of sterically stabilized colloidal silica particles of three different sizes at volume fractions above 0.5. Despite a small surface charge, which elevated the intrinsic viscosity from the Einstein value of 2.5, the particles were found to behave essentially as hard spheres in the concentrated suspensions and to have properties highly reminiscent of molecular glasses. The zero shear rate viscosity, characteristic of disordered suspensions and present at all volume fractions, diverges as φ → 0.6 and is well-described by the Doolittle equation for glassy flow. For suspensions with a relative zero shear rate viscosity greater than 5 × 102, shear thickening was observed. Characteristic time scales for particle rearrangement determined from critical shear rates for shear thinning and shear thickening were found to follow trends predicted for molecular glasses. A transition from a liquidlike linear relaxation response to glassy stretched exponential behavior was observed as volume fraction was increased. The onset of the glassy relaxation response, indicative of nondecaying correlations, occurred near a volume fraction of 0.52. © 1990 American Chemical Society.