RHEOLOGICAL AND MICROSTRUCTURAL TRANSITIONS IN COLLOIDAL CRYSTALS

The flow of suspensions of 229-nm, charge-stabilized, polystyrene latex particles is directly linked with suspension microstructure. Transitions from long-range orientational order at rest to a steady-state, polycrystalline phase are associated with exceeding the dynamic yield stress. Application of stresses larger than a critical value nucleates a sliding layer microstructure which is accompanied by a discontinuous drop in suspension viscosity. Over a range of shear rates, polycrystalline and sliding layer microstructures coexist. At elevated shear rates, stresses and microstructures fluctuate in time. Shear thickening accompanies the complete loss of long-range orientational order. The transitions in rheology and microstructure are reversible except at very high shear rates where shear thickening accompanies irreversible flocculation.