The significance of shear stress in the agglomeration kinetics of fractal aggregates

The aggregation kinetics of fully destabilized colloidal hematite particles under conditions of varying laminar shear stress were investigated. Particle size distributions were measured over time, which allowed for a mechanistic evaluation of various aggregate-aggregate interaction rates. It was observed experimentally that large aggregates react rapidly with sub-micron size fractions under conditions of an applied shear stress; Brownian motion appears to dominate interactions only at early times when a monomodal size distribution exists. It was hypothesized that collisions between dissimilar sized aggregates are favored under laminar shear conditions. The experimental results also suggest that hydrodynamic influences are less important when porous, fractal aggregates are interacting than in interactions between impermeable spheres. (C) 1998 Elsevier Science Ltd. All rights reserved.