THE SIGNIFICANCE OF SHEAR-STRESS IN THE AGGLOMERATION KINETICS OF FRACTAL AGGREGATES

The aggregation kinetics of fully destabilized colloidal hematite part icles under conditions of varying laminar shear stress were investigat ed. Particle size distributions were measured over time, which allowed for a mechanistic evaluation of various aggregate-aggregate interacti on rates. It was observed experimentally that large aggregates react r apidly with sub-micron size fractions under conditions of an applied s hear stress; Brownian motion appears to dominate interactions only at early times when a monomodal size distribution exists. It was hypothes ized that collisions between dissimilar sized aggregates are favored u nder laminar shear conditions. The experimental results also suggest t hat hydrodynamic influences are less important when porous, fractal ag gregates are interacting than in interactions between impermeable sphe res. (C) 1998 Elsevier Science Ltd. All rights reserved.