The flow anisotropy of a concentrated colloidal suspension at the jamming transition is studied. It is shown that the use of rough spherical particles reduces the hydrodynamic lubrication forces between adjacent colloids and makes possible the study of the stress tensor anisotropy. At low shear rates, the suspension exerts an attractive force between two opposite surfaces, whereas at higher shear rates it becomes dilatant. Direct confocal microscopy observation of the particles organization reveal that crystallites form at high shear rate.

• Received 4 August 2005

DOI:https://doi.org/10.1103/PhysRevLett.95.268302