Formation of stable aggregates by fluid-assembled solid bridges

TL;DR

This study investigates how fluid-assembled solid bridges form during drying, creating stable, hierarchical aggregates with cohesion primarily dependent on grain size, which has implications for natural and synthetic material stability.

Contribution

It reveals the formation mechanism of solid bridges during evaporation-driven aggregation and quantifies their strength and hierarchical structure, advancing understanding of cohesion in particulate materials.

Findings

Cohesion occurs at ~5 μm length scale where attractive forces surpass particle weight.

Smaller particles condense within capillary bridges to form stabilizing solid bridges.

Hierarchical clusters exhibit strong cohesion based on grain size, not mineralogy.

Abstract

When a colloidal suspension is dried, capillary pressure may overwhelm repulsive electrostatic forces, assembling aggregates that are out of thermal equilibrium. This poorly understood process confers cohesive strength to many geological and industrial materials. Here we observe evaporation-driven aggregation of natural and synthesized particulates, probe their stability under rewetting, and measure bonding strength using an atomic force microscope. Cohesion arises at a common length scale (~ 5 um), where interparticle attractive forces exceed particle weight. In polydisperse mixtures, smaller particles condense within shrinking capillary bridges to build stabilizing 'solid bridges' among larger grains. This dynamic repeats across scales forming remarkably strong, hierarchical clusters, whose cohesion derives from grain size rather than mineralogy. Results may help to understand and control the stability of natural soils and synthetic materials.