Theoretical consideration of the rheological properties of aggregated suspensions

Abstract

The rheological properties of particulate dispersions containing aggregate structures were theoretically investigated in this study. Under the assumption of Stokes flow, the viscosity of fluids with fine particles was derived by a theoretical method based on the multipole expansion in reciprocal space. In this method, many-body hydrodynamic interactions were considered as the multipole-expanded moment of the force density at the surface of the particles. It is possible to calculate the viscosity of particulate suspensions by considering higher-order moments. The viscosity of monodisperse particulate suspensions was calculated under various conditions. To verify the accuracy of the calculation, the viscosity of uniformly distributed particulate suspensions was calculated, and the results were compared with the experimental results of previous studies. The calculated viscosities were in good agreement with the experimental results for a wide range of particle volumetric concentrations. The viscosity of aggregated suspensions was also calculated to examine the mechanism of viscosity change. The viscosity was systematically calculated with changing the aggregate size and particle concentration. The results indicate that the hydrodynamic effect is not significant on the viscosity change by aggregation, which is contrary to the assumption of previous viscosity models. The calculation results suggest that the increase in the viscosity of aggregated suspensions is instead caused by the direct influence of inter-particle forces.