STRUCTURAL-CHANGES AND ORIENTATIONAL ORDER IN A SHEARED COLLOIDAL SUSPENSION

Small-angle neutron scattering experiments were carried out on a charged-stabilized dense colloidal suspension to observe changes in lattice structure as a function of shear rate. It is shown that (1) the lattice will evolve from a crystalline state in equilibrium to a polycrystalline state if subjected to a very low shear; and (2) as the shear is increased, partial order is reestablished with the apparent appearance of sliding layer flow. The transitions are reversible. The first transition occurs when the dynamic yield stress is exceeded; the second is discontinuous and is associated with an anomalous flow region in which the stress decreases with increasing shear rate.