Equilibrium concentration profiles and sedimentation kinetics of colloidal gels under gravitational stress

TL;DR

This paper investigates the sedimentation behavior of colloidal gels under gravity, revealing universal scaling laws for concentration profiles and detailing the stages of gel collapse through combined experimental and theoretical analysis.

Contribution

It demonstrates a universal scaling of concentration profiles based on a power law of the elastic modulus and provides a comprehensive kinetic description of gel sedimentation.

Findings

Profiles collapse onto a master curve with reduced variables

Sedimentation involves latency, rapid collapse, and final relaxation stages

Elastic modulus follows a power law with volume fraction

Abstract

We study the sedimentation of colloidal gels by using a combination of light scattering, polarimetry and video imaging. The asymptotic concentration profiles $\varphi(z,t\rightarrow \infty)$ exhibit remarkable scaling properties: profiles for gels prepared at different initial volume fractions and particle interactions can be superimposed onto a single master curve by using suitable reduced variables. We show theoretically that this behavior stems from a power law dependence of the compressive elastic modulus \textit{vs} $\varphi$, which we directly test experimentally. The sedimentation kinetics comprises an initial latency stage, followed by a rapid collapse where the gel height $h$ decreases at constant velocity, and a final compaction stage characterized by a stretched exponential relaxation of $h$ towards a plateau. Analogies and differences with previous works are briefly discussed.