Role of lubricated contacts in concentrated polydisperse suspensions

In this article experimental results of the bulk behavior of concentrated suspensions of coarse and fine (colloidal) particles in a Newtonian fluid (water) are presented. Different theological behaviors can be observed depending on both the solid concentrations in fine and coarse particles and the shear velocity. For suspensions concentrated in coarse particles that are poor in fine particles, the bulk behavior is frictional for low shear velocities and viscous for sufficiently large shear velocities. In the converse case, for mixtures rich in fine particles, the bulk behavior is viscoplastic. A more complex time-dependent behavior can be observed when the viscoplastic force exerted by the dispersion on coarse particles roughly balances the force of gravity. The diversity in bulk behavior is explained by the specific role played by the contact between coarse particles. (C) 2001 The Society of Rheology.