Effects of particle properties on the rheology of concentrated noncolloidal suspensions

Abstract

A concise review of the literature and new experimental results are given concerning the effects of particle shape, density, size, and surface charge on the rheology of concentrated noncolloidal suspensions. While the literature review covered both Newtonian and non‐Newtonian liquid media, the experimentation was focused on Newtonian liquid media and shear rates ranging from 1 to 2000 s−1. Rheological similarities regarding these effects exist between the concentrated suspensions in Newtonian liquid media with viscosities as low as 3 cP and those in polymeric media with viscosities as high as 5×104 P. The measured relative viscosity of a nonaggregated Newtonian suspension as a function of particle volume fraction was found to agree well with the predictions of both the Krieger–Dougherty and the Maron–Pierce–Kitano equations. Also, the sole parameter of the former equation, maximum packing fraction, was found to be in much better agreement with that determined from sedimentation than that of the latter equation. In addition, we found that the relative viscosity of a pseudoplastic noncolloidal suspension correlates well with the particle Peclet number for both spherical and irregularly shaped particles even though Brownian motion is negligible. Specifically, since particle diffusional relaxation time increases with particle radius cubed, larger particles in an aggregated system diffuse to a lesser extent than smaller particles within the same time scale of shear, and less energy is dissipated as a result. Particle density, up to 2.5 g/cc, was found to have no effect on the relative viscosity.