Validity of the Cox–Merz rule for concentrated suspensions

Abstract

The flow behavior of glass bead, limestone, and powdered quartz suspensions was examined in steady and oscillatory shear tests. The solids content was varied up to a maximum of 25 vol % and the mean particle diameter ranged from 3 to 31 μm. The suspending liquid consisted of one of two silicone oils, which had limiting viscosities at zero shear rate slightly greater than 5×105 and 106 mPa s, respectively. The concept of shear stress equivalent inner shear rate, which describes the response of suspensions in steady shear experiments, was applied here to dynamic tests. Application of this concept yielded uniform descriptions of the flow curves that result from oscillatory deformations. In the region dominated by hydrodynamic forces, a modified Cox–Merz rule was derived. The shear stress function τ(γ) and complex modulus G*(ω) can be expressed as a function of the solid concentration using the parameters in this modified Cox–Merz relation.