Abstract
The rheological behavior of two highly concentrated composites (suspensions) were investigated in capillary and parallel disk torsional flows. Suspension I was bimodal in particle size distribution and contained 76.5% solids by volume. Suspension II was unimodal with 60% solids by volume. It was found that flow of the suspensions were strongly affected by slip at the walls of the instrument. The slip mechanism is thought to be caused by the formation of an “apparent slip layer” near the walls which mainly consists of the suspending medium. The slip velocity determined was found to be approximately linear with the shear stress at the wall in both types of flows. Suspension I exhibited Newtonian behavior at low shear stresses, but became pseudoplastic at high shear stresses. Suspension II was shear thinning at low shear stresses, but shear thickening at high shear stresses. The contribution of slip to the volumetric flow rate in capillary flows decreased with the shear stress at the wall in suspension I, whereas it increased with the shear stress at the wall in suspension II. This indicates that the contribution of slip to the total volumetric flow rate is more significant when the suspension exhibits higher viscosity. The flow was pluglike owing to slip at low shear stresses in suspension I and at high shear stresses in suspension II.
Published Version
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