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

Shear viscosity and wall slip of dense suspensions of a silicone polymer incorporated with polydisperse particles were investigated. Three types of particles with low aspect ratios were used to achieve a relatively high maximum packing fraction of 0.86. Such a high maximum packing fraction allowed the preparation of suspensions with a wide range of solid volume fractions in the range of 0.62 to 0.82. The wall slip velocities of the suspensions in steady torsional and capillary flows were characterized and determined to be fully consistent with the mechanism of apparent slip layer formation at the wall. Upon wall slip corrections it was found that at shear stresses which are significantly above the yield stress the relative shear viscosity of the suspensions obeys well the Krieger-Dougherty relationship that links the relative shear viscosity behavior of dense suspensions solely to the ratio of the volume fraction over the maximum packing fraction of solids. However, at lower shear stresses that are in the vicinity of the yield stresses the relative shear viscosity becomes functions of both the ratio of the volume fraction over the maximum packing fraction and the shear stress. It is clearly demonstrated that without wall slip analysis the accurate characterization of the relative shear viscosity of dense suspensions is not possible.