Rheology of sedimenting particle pastes

TL;DR

This paper investigates how non-density-matched suspensions exhibit a critical shear rate that determines whether they sediment or are homogenized, based on a balance of viscous and gravitational forces.

Contribution

It introduces a simple scaling model that predicts the critical shear rate in sedimenting suspensions, validated by diverse experimental data.

Findings

Critical shear rate exists for sedimenting suspensions.

Critical shear rate depends on viscous and gravitational forces.

Model accurately predicts experimental results.

Abstract

We study the local and global rheology of non-Brownian suspensions in a solvent that is not density-matched, leading to either creaming or sedimentation of the particles. Both local and global measurements show that the incomplete density matching leads to the appearance of a critical shear rate above which the suspension is homogenized by the flow, and below which sedimentation or creaming happens. We show that the value of the critical shear rate and its dependence on the experimental parameters are governed by a simple competition between the viscous and gravitational forces, and present a simple scaling model that agrees with the experimental results from different types of experiments (local and global) in different setups and systems.