Correlating inter-particle forces and particle shape to shear-induced aggregation/fragmentation and rheology for dilute anisotropic particle suspensions: A complementary study via capillary rheometry and in-situ small and ultra-small angle X-ray scattering

Hypothesis: Understanding the stability and rheological behavior of suspensions composed of anisotropic particles is challenging due to the complex interplay of hydrodynamic and colloidal forces. We propose that orientationally-dependent interactions resulting from the anisotropic nature of non-spherical subunits strongly influences shear-induced particle aggregation/fragmentation and suspension rheological behavior. Experiments: Wide-, small-, and ultra-small-angle X-ray scattering experiments were used to simultaneously monitor changes in size and fractal dimensions of boehmite aggregates from 6 to 10,000 A as the sample was recirculated through an in-situ capillary rheometer. The latter also provided simultaneous suspension viscosity data. Computational fluid dynamics modeling of the apparatus provided a more rigorous analysis of the fluid flow. Findings: Shear-induced aggregation/fragmentation was correlated with a complicated balance between hydrodynamic and colloidal forces. Multi-scale fractal aggregates formed in solution but the largest could be fragmented by shear. Orientationally-dependent interactions lead to a relatively large experimental suspension viscosity when the hydrodynamic force was small compared to colloidal forces. This manifests even at low boehmite mass fractions. (C) 2020 Published by Elsevier Inc.