Dense suspensions with high solid volume fractions (φ≥0.5) can exhibit complex rheological behaviors, including both shear thinning and subsequent shear thickening over a range of increasing shear rates. Understanding the mechanisms behind these rheological behaviors can improve the design of materials systems that behave as predicted and desired under process flows. Here, we present a study on an industrially relevant, dense (φ=0.5), colloidal alumina suspension and show how the addition and loading of a non-adsorbing polyvinylpyrrolidone (PVP) at different molecular weights can be used to tune and control its rheological properties. PVP was added at varying concentrations spanning the dilute and semi-dilute, non-entangled regimes for each molecular weight. The addition of PVP at concentrations in the dilute regime was shown to increase the viscosity of the suspension and induce discontinuous shear thickening (DST). However, further increases in PVP loading, particularly at higher molecular weights and within the semi-dilute, non-entangled regime, also increased the dynamic yield stress of the material, made the suspension more shear thinning, and delayed the onset of DST. Rheological measurements were coupled with insights on the relevant particle and polymer length scales from small angle neutron scattering (SANS), including Rheo-SANS measurements, to inform on the mechanisms by which non-adsorbing polymers influence suspension rheology across multiple flow regimes.
