Jamming, two-fluid behaviour and 'self-filtration' in concentrated particulate suspensions

TL;DR

This paper investigates how concentrated colloidal suspensions flow through constrictions, revealing jamming and unjamming phenomena that lead to a self-filtration effect, linking jamming behavior with a two-fluid flow model.

Contribution

It introduces the concept of self-filtration in colloidal suspensions due to jamming and unjamming, connecting microscopic observations with a two-fluid flow framework.

Findings

Jamming and unjamming occur above a critical volume fraction.

Flow causes a reduction in colloid concentration downstream.

Flow involves a combination of solid-like jamming and solvent flow.

Abstract

We study the flow of model experimental hard sphere colloidal suspensions at high volume fraction $\Phi$ driven through a constriction by a pressure gradient. Above a particle-size dependent limit $\Phi_0$, direct microscopic observations demonstrate jamming and unjamming--conversion of fluid to solid and vice versa--during flow. We show that such a jamming flow produces a reduction in colloid concentration $\Phi_{x}$ downstream of the constriction. We propose that this `self-filtration' effect is the consequence of a combination of jamming of the particulate part of the system and continuing flow of the liquid part, i.e. the solvent, through the pores of the jammed solid. Thus we link the concept of jamming in colloidal and granular media with a 'two-fluid'-like picture of the flow of concentrated suspensions. Results are also discussed in the light of Osborne Reynolds' original experiments on dilation in granular materials.