Rheology of bidisperse suspensions at the colloidal-to-granular transition

TL;DR

This study uses particle-based simulations to explore how mixtures of colloids and grains behave rheologically, revealing complex viscosity responses and flowability depending on composition and shear rate.

Contribution

It provides a new constitutive model describing the rheology of bidisperse suspensions across the colloidal-to-granular transition, considering shear rate and composition effects.

Findings

Viscosity increases monotonically with added grains at low shear rates.

Nonmonotonic viscosity response when adding colloids to grains.

Flowability can be enhanced by increasing solids content in certain regimes.

Abstract

We use particle-based simulation to study the rheology of dense suspensions comprising mixtures of small colloids and larger grains, which exhibit shear thinning at low shear rates and shear thickening at high shear rates. By systematically varying the volume fraction of the two species, we demonstrate a monotonic increase in viscosity when grains are added to colloids, but, conversely, a nonmonotonic response in both the viscosity and shear thickening onset when colloids are added to grains. Both effects are most prominent at intermediate shear rates where diffusion and convection play similar roles in the dynamics. We rationalise these results by measuring the maximum flowable volume fraction as functions of the Peclet number and composition, showing that in extreme cases increasing the solids content can allow a jammed suspension to flow. These results establish a constitutive description for the rheology of bidisperse suspensions across the colloidal-to-granular transition, with implications for flow prediction and control in multicomponent particulate systems.