Formation of stable aggregates by fluid-assembled solid bridges

Area of Science:

• Colloid and Surface Science
• Materials Science
• Geophysics

Background:

• Capillary pressure during drying can overcome electrostatic forces in colloidal suspensions.
• This process leads to the formation of non-equilibrium aggregates, contributing to the strength of geological and industrial materials.
• The mechanisms behind this aggregation and the resulting cohesive strength are not fully understood.

Purpose of the Study:

• To investigate the process of evaporation-driven aggregation in natural and synthesized particulates.
• To analyze the stability of these aggregates upon rewetting.
• To quantify the bonding strength of the aggregated particles.

Main Methods:

• Observation of evaporation-driven aggregation.
• Stability testing under rewetting conditions.
• Atomic force microscopy to measure interparticle bonding strength.

Main Results:

• Cohesion is observed at a characteristic length scale of approximately 5 μm, where attractive forces dominate particle weight.
• In polydisperse mixtures, smaller particles accumulate in capillary bridges, forming solid bridges that stabilize larger grains.
• Hierarchical clusters with significant cohesive strength are formed, with strength dependent on grain size rather than mineralogy.

Conclusions:

• Evaporation-driven aggregation creates robust, hierarchical structures in polydisperse particulate systems.
• The formation of solid bridges by smaller particles is a key mechanism for enhancing cohesion.
• Understanding this process is crucial for predicting the strength and erodibility of soils and other particulate materials.