The mechanisms of gravity-constrained aggregation in natural colloidal suspensions

Colloidal settlement in natural aqueous suspensions is effectively compensated by diffusive movement if particles resist aggregation - a state known as colloidal stability. However, if the settling velocity increases upon aggregation, complex structural features emerge from the directional movement induced by gravity. We present a comprehensive modeling study on the evolution of an aggregated three-dimensional structure due to diffusion, surface interactions, and gravity. The systematic investigation of particle geometry and size revealed three mechanisms: (I) aggregation due to spatial confinement of settled particles, (II) aggregation due to differential settling, whereby fast and slow particles collide, (III) inhibition of aggregation due to fractionation of particles with different settling velocity. A 3D visu-alization tool allowed us to follow the subtle interplay of these mechanisms and the highly dynamic hier-archical self-assembly of aggregates. It revealed how the balance of the different interactions determines the actual rate of aggregation. (c) 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

A comprehensive modeling study on the evolution of an aggregated three-dimensional structure due to diffusion, surface interactions, and gravity revealed three mechanisms of aggregation and showed how the balance of different interactions determines the rate of aggregation. The 3D visualization tool allowed tracking of subtle interplay of mechanisms and dynamic hierarchical self-assembly of aggregates.