A unified description of the rheology of hard-particle suspensions

TL;DR

This paper investigates the rheology of hard-particle suspensions across a wide size range, revealing shear thickening as the key transition mechanism and providing a unified theoretical framework for their flow behavior.

Contribution

It offers the first comprehensive experimental study bridging colloidal and granular suspension rheology, and validates a new friction-based shear thickening theory.

Findings

Shear thickening drives the transition across particle sizes.

Unified rheological description for the full size spectrum.

Experimental validation of a friction-induced shear thickening model.

Abstract

The rheology of suspensions of Brownian, or colloidal, particles (diameter $d \lesssim 1$ $\mu$m) differs markedly from that of larger grains ($d \gtrsim 50$ $\mu$m). Each of these two regimes has been separately studied, but the flow of suspensions with intermediate particle sizes (1 $\mu\textrm{m} \lesssim d \lesssim 50$ $\mu$m), which occur ubiquitously in applications, remains poorly understood. By measuring the rheology of suspensions of hard spheres with a wide range of sizes, we show experimentally that shear thickening drives the transition from colloidal to granular flow across the intermediate size regime. This insight makes possible a unified description of the (non-inertial) rheology of hard spheres over the full size spectrum. Moreover, we are able to test a new theory of friction-induced shear thickening, showing that our data can be well fitted using expressions derived from it.