Shear viscosity and wall slip behavior of dense suspensions of polydisperse particles

The significant problem of wall slip and shear viscosity of dense suspensions is addressed using steady torsional and capillary flows of a silicone polymer, incorporated with polydisperse particles with low aspect ratios, to achieve a relatively high maximum packing fraction, φ m = 0.86. Such a high φ m allowed the preparation of well-mixed suspensions with a wide range of solid volume fractions, φ, i.e., 0.62 ≤ φ ≤ 0.82. It is demonstrated that the characterization of the relative viscosity and yield stresses of the particulate suspensions requires a proper treatment of wall slip effects. The wall slip velocity versus the shear stress relationship is governed by the apparent slip mechanism and is predictable using the shear viscosity of the binder and the thickness of the apparent slip layer. At shear stresses which are significantly above the yield stress, the relative shear viscosity of the suspensions depends solely on φ / φ m. However, at lower shear stresses that are in the vicinity of the yield stresses, the relative shear viscosity becomes functions of both φ / φ m and the shear stress.