  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.
