RHEOLOGICAL AND MICROSTRUCTURAL TRANSITIONS IN COLLOIDAL CRYSTALS

The flow of suspensions of 229-nm, charge-stabilized, polystyrene late x particles is directly linked with suspension microstructure. Transit ions from long-range orientational order at rest to a steady-state, po lycrystalline phase are associated with exceeding the dynamic yield st ress. 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, polycrystal line and sliding layer microstructures coexist. At elevated shear rate s, stresses and microstructures fluctuate in time. Shear thickening ac companies the complete loss of long-range orientational order. The tra nsitions in rheology and microstructure are reversible except at very high shear rates where shear thickening accompanies irreversible flocc ulation.