Stress distributions in flowing aggregated colloidal suspensions

Simulations of the flow of concentrated aggregated colloidal systems, at th e particulate level, are used to investigate the distribution of stresses i n the shear-thinning regime. It is found that the distribution of shear str ess carried by interparticle bonds decays approximately exponentially at la rge stresses, but with a double-exponential distribution for values of posi tive stress. The microstructural mechanisms associated with large stresses are manifested in clusters which dominate the positive contribution to the stress in the system. Towards the end of shear thinning the highest forces occur along bonds defining rods of particles aligned approximately along th e flow-compression direction. We propose that the rheology of such systems is determined by a rupture-reformation process of these clusters of stress concentration during the flow. The aggregation forces play the role of enha ncing such stress concentration by stabilizing clusters against buckling. ( C) 1999 American Institute of Physics. [S0021-9606(99)51934-X].