Colloidal gel elasticity arises from the packing of locally glassy clusters

Abstract

Colloidal gels formed by arrested phase separation are found widely in agriculture, biotechnology, and advanced manufacturing; yet, the emergence of elasticity and the nature of the arrested state in these abundant materials remains unresolved. Here, the quantitative agreement between integrated experimental, computational, and graph theoretic approaches are used to understand the arrested state and the origins of the gel elastic response. The micro-structural source of elasticity is identified by the l -balanced graph partition of the gels into minimally interconnected clusters that act as rigid, load bearing units. The number density of cluster-cluster connections grows with increasing attraction, and explains the emergence of elasticity in the network through the classic Cauchy-Born theory. Clusters are amorphous and iso-static. The internal cluster concentration maps onto the known attractive glass line of sticky colloids at low attraction strengths and extends it to higher strengths and lower particle volume fractions.

Time-rate-transformation framework for targeted assembly of short-range attractive colloidal suspensions

“…where Z∞ is the average coordination number of a hard-sphere suspension at a given shear rate ( are not sufficient to break the particulate network globally, they provide the particles near the surface of locally-glassy clusters [45] with additional energy required to occasionally break their bonding interactions and explore a more stable global state with progressively larger number of bonds [12,18]. Recently, Whitaker et al [45] through graph theory and structural analysis of the particle configurations showed that in gels formed under quiescent conditions as well as under flowing conditions, the elasticity of the gel arises from the packing of locally glassy clusters.…”

“…shear viscosity, loss and storage moduli, as well as electrical conductivity. Furthermore, fast confocal microscopy of sheared attractive colloids have also shown the role of prior shear history and the rate of applied deformation in controlling the microstructural evolutions of colloidal gels under flow [25,27,45].…”

Contact and macroscopic ageing in colloidal suspensions

“…double-layer polarization); in such cases, only moderate levels of attraction may be introduced, e.g. via polymer depletion effects [8][9][10][11][12]. Confocal microscopy was instrumental to these advances, yet may only be applied to transparent, index matched, systems, in which van der Waals forces are essentially absent.…”

Viscoelastic cluster densification in sheared colloidal gels

“…It can be expected that these denser network building blocks increase the percolation threshold when compared at overall volume fraction. On the other hand, recent work on colloidal gels 48 has demonstrated that gel elasticity is controlled by the volume fraction of locally isostatic clusters, which can be expected to increase more strongly with volume fraction in the denser systems. Here, the change in percolation threshold and volume fraction dependency of gel elasticity are shown to be linked.…”

“…The number of particle-particle contacts between clusters and the interaction between two particles at contact are found to be the source leading to the gel's elasticity. [46][47][48] The flow history also plays an important role. Koumakis et al showed that fully breaking the structure leads to more homogeneous and stronger gels, whereas preshear at low rates creates largely heterogeneous weaker gels with reduced elasticity.…”