Role of lubricated contacts in concentrated polydisperse suspensions

In this article experimental results of the bulk behavior of concentrated s uspensions of coarse and fine (colloidal) particles in a Newtonian fluid (w ater) are presented. Different theological behaviors can be observed depend ing on both the solid concentrations in fine and coarse particles and the s hear velocity. For suspensions concentrated in coarse particles that are po or in fine particles, the bulk behavior is frictional for low shear velocit ies and viscous for sufficiently large shear velocities. In the converse ca se, for mixtures rich in fine particles, the bulk behavior is viscoplastic. A more complex time-dependent behavior can be observed when the viscoplast ic force exerted by the dispersion on coarse particles roughly balances the force of gravity. The diversity in bulk behavior is explained by the speci fic role played by the contact between coarse particles. (C) 2001 The Socie ty of Rheology.