Formation of stable aggregates by fluid-assembled solid bridges

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 μm), 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. These results may help toward understanding the strength and erodibility of natural soils, and other polydisperse particulates that experience transient hydrodynamic forces.

Step-Wise Deposition Process for Dielectrophoretic Formation of Conductive 50-Micron-Long Carbon Nanotube Bridges

“…As the liquid surrounding the CNTs evaporates, the surface tension of these shrinking droplets pulls CNTs together as depicted in Figure 9, leading to a dramatic increase in conductivity of CNT bridges. This formation of microaggregates due to surface tension during solvent evaporation was observed by other researchers [35].…”

“…conductivity of CNT bridges. This formation of microaggregates due to surface tension during solvent evaporation was observed by other researchers [35]. It is clear that as a result of the heat treatment (200 • C for 20 min), the resistance of the CNT bridges decreases dramatically.…”

Moisture alone is sufficient to impart strength but not weathering resistance to termite mound soil

“…Study with bidispersed (particles of two sizes) suspension of silica spheres in water shows that as water evaporates, the receding contact line of water drags smaller particles near the larger particles, forming size-segregated aggregates where the large particles are ringed by smaller particles which in turn are ringed by even smaller particles [ 45 ]. After water evaporation solid bridges are formed, connecting larger particles to the substrate and to each other forming aggregates [ 45 ]. This brings particles within the range of van der Waals interactions which are enhanced by dehydration [ 45 ].…”

“…After water evaporation solid bridges are formed, connecting larger particles to the substrate and to each other forming aggregates [ 45 ]. This brings particles within the range of van der Waals interactions which are enhanced by dehydration [ 45 ]. The aggregates formed in this manner were stable when subjected to rewetting [ 45 ].…”

“…This brings particles within the range of van der Waals interactions which are enhanced by dehydration [ 45 ]. The aggregates formed in this manner were stable when subjected to rewetting [ 45 ]. This is similar to the case of termite mounds where a range of particle sizes [ 32 ], in the presence of moisture [ 30 ], is used by termites for construction.…”