The Role of Solid Friction in the Sedimentation of Strongly Attractive Colloidal Gels

TL;DR

This study investigates how solid friction influences the long-term sedimentation behavior of strongly attractive colloidal gels, revealing a linear relationship between initial and final heights and a dependence of wall friction on volume fraction.

Contribution

It introduces a model linking gel height, gravity, elasticity, and wall friction, highlighting the volume fraction's effect on static friction strength.

Findings

Asymptotic gel height varies linearly with initial height.

Solid friction between gel and container walls decreases with increasing volume fraction.

A simple model explains the balance of forces governing sedimentation.

Abstract

We study experimentally and theoretically the sedimentation of gels made of strongly aggregated colloidal particles, focussing on the long time behavior, when mechanical equilibrium is asymptotically reached. The asymptotic gel height is found to vary linearly with the initial height, a finding in stark contrast with a recent study on similar gels [Manley \textit{et al.} 2005 \textit{Phys. Rev. Lett.} \textbf{94} 218302]. We show that the asymptotic compaction results from the balance between gravity pull, network elasticity, and solid friction between the gel and the container walls. Based on these ingredients, we propose a simple model to account for the dependence of the height loss on the initial height and volume fraction. As a result of our analysis, we show that the static friction coefficient between the gel and the container walls strongly depends on volume fraction: the higher the volume fraction, the weaker the solid friction. This nonintuitive behavior is explained using simple scaling arguments.