Abstract
The rheological and microstructural properties of dense suspensions of uniform, charge stabilized colloidal spheres with diameters greater than 200 nm are investigated at volume fractions just below the ordering transition up to 0.6. Shear stresses marking static and dynamic yielding, discontinuous shear thinning, and shear thickening are weakly dependent on volume fraction and particle size when scaled on the crystal’s elastic modulus G0. As shear stress is increased microstructures evolve through similar states independent of volume fraction. As rest, presheared suspensions exhibit long‐range orientational order. Above the dynamic yield stress, the suspensions deform with a polycrystalline microstructure which, at intermediate shear rates, evolves to hexagonally close‐packed planes lying parallel to the rheometer walls. At higher shear rates the suspensions melt. Thickening is only observed above a volume fraction of 0.4–0.5, depending on particle size and at shear rates above that where the hexagonal close packing has been degraded. Shear rates characteristic of changes in flow properties and microstructure increase exponentially with volume fraction in the same manner as G0. As a consequence, a volume fraction independent constitutive response is observed when stress is scaled on G0 and the shear rate is scaled on G0/μ. Here μ is the continuous phase viscosity.
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