Network Topology in Soft Gels: Hardening and Softening Materials

Bouzid, Mehdi; Gado, Emanuela Del

doi:10.1021/acs.langmuir.7b02944

Cited by 77 publications

(98 citation statements)

References 64 publications

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“…The attractive gel model further demonstrates that such structural correlations and heterogeneities can naturally arise as a result of short range attractive interactions in a thermal system. Deeper understandings of how this structural heterogeneity develops in the incipient phase separation and how it depends on the preparation protocol used for the gel (for example, the cooling rate in the simulations) [53], as well as connecting correlated RP scenario obtained here to the hard sphere limit where no attraction is present and rigidity emerges at the random close packing volume fraction (84% in 2D) or to the case in which different types of topological constraints may be present [54], will be intriguing topics to explore in future studies. town Environmental Initiative and Georgetown University, Kavli Institute for Theoretical Physics at the University of California Santa Barbara and National Science Foundation (Grant No.…”

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confidence: 77%

Correlated Rigidity Percolation and Colloidal Gels

Zhang

Bouzid

et al. 2019

Phys. Rev. Lett.

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Rigidity percolation (RP) occurs when mechanical stability emerges in disordered networks as constraints or components are added. Here we discuss RP with structural correlations, an effect ignored in classical theories albeit relevant to many liquid-to-amorphous-solid transitions, such as colloidal gelation, which are due to attractive interactions and aggregation. Using a lattice model, we show that structural correlations shift RP to lower volume fractions. Through molecular dynamics simulations, we show that increasing attraction in colloidal gelation increases structural correlation and thus lowers the RP transition, agreeing with experiments. Hence colloidal gelation can be understood as a RP transition, but occurs at volume fractions far below values predicted by the classical RP, due to attractive interactions which induce structural correlation. arXiv:1807.08858v1 [cond-mat.soft]

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confidence: 77%

Correlated Rigidity Percolation and Colloidal Gels

Zhang

Bouzid

et al. 2019

Phys. Rev. Lett.

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“…The rotational and translational diffusion coefficients D R and D T are related by the identity σ 2 D R /3 = time is τ = mσ 2 / , but a more useful choice is the Brownian relaxation time τ R = σ 2 /4D T , which is the time taken for a particle to move a distance equal to its own diameter [15]; most temporal quantities are therefore reported in units of τ R . ξ T is set to 10.0 mτ −1 (thus, ξ R = 10/3 mτ −1 σ 2 ) in all simulations, which is in the range commonly seen in the gel simulation literature [47,58]. The integration time step is 25 × 10 −4 τ in simulations of gelation or low-frequency shear, and 1 × 10 −4 τ in simulations of high-frequency shear, discussed further below.…”

Section: Simulation Protocolmentioning

confidence: 99%

Computer simulations of colloidal gels: how hindered particle rotation affects structure and rheology

et al. 2020

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The effects of particle roughness and short-ranged non-central forces on colloidal gels are studied using computer simulations in which particles experience a sinusoidal variation in energy as they rotate. The number of minima n and energy scale K are the key parameters; for large K and n, particle rotation is strongly hindered, but for small K and n particle rotation is nearly free.A series of systems are simulated and characterized using fractal dimensions, structure factors, coordination number distributions, bond-angle distributions and linear rheology. When particles rotate easily, clusters restructure to favor dense packings. This leads to longer gelation times and gels with strand-like morphology. The elastic moduli of such gels scale as G ∝ ω 0.5 at high shear frequencies ω. In contrast, hindered particle rotation inhibits restructuring and leads to rapid gelation and diffuse morphology. Such gels are stiffer, with G ∝ ω 0.35 . The viscous moduli G in the low-barrier and high-barrier regimes scale according to exponents 0.53 and 0.5, respectively.The crossover frequency between elastic and viscous behaviors generally increases with the barrier to rotation. These findings agree qualitatively with some recent experiments on heterogeneouslysurface particles and with studies of DLCA-type gels and gels of smooth spheres. arXiv:1909.01491v1 [cond-mat.soft] 3 Sep 2019Key simulation parameters are summarized in Table I. Because the particles are monodisperse, they all have the same mass m. All quantities are reported in reduced units, with temperature scaled by , distance scaled by the particle diameter σ. The reduced unit for

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“…Numerical studies in Zhang et al [13], on the other hand, focused on how the nonlinear alignment of springs in a randomly diluted triangular lattice controls the transition at connectivities below what is known as the central force rigidity percolation point. Finally, Bouzid and Del Gado [14] focused on the role of connectivity in a disordered system, by studying the mechanical * corresponding author: Estelle Berthier (ehberthi@ncsu.edu) properties of simulated soft gels, showing that the topology greatly affects stress redistribution and deformation of the branches, resulting in brittle failure of the more homogeneous stiffer gels with higher mean connectivity.…”

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Rigidity percolation control of the brittle-ductile transition in disordered networks

Berthier

Kollmer

Henkes

et al. 2019

Phys. Rev. Materials

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In ordinary solids, material disorder is known to increase the size of the process zone in which stress concentrates at the crack tip, causing a transition from localized to diffuse failure. Here, we report experiments on disordered 2D lattices, derived from frictional particle packings, in which the mean coordination number z of the underlying network provides a similar control. Our experiments show that tuning the connectivity of the network provides access to a range of behaviors from brittle to ductile failure. We elucidate the cooperative origins of this transition using a frictional pebble game algorithm on the original, intact lattices. We find that the transition corresponds to the isostatic value z = 3 in the large-friction limit, with brittle failure occurring for structures vertically spanned by a rigid cluster, and ductile failure for floppy networks containing nonspanning rigid clusters. Furthermore, we find that individual failure events typically occur within the floppy regions separated by the rigid clusters. Materials as varied as semiconductors [1], aqueous foams [2], polymers [3], metals [4] and rocks[5] exhibit a brittle-ductile transition when parameters such as geometry, temperature, pressure, loading rate, or even illumination are varied. Because brittle failure occurs suddenly and unpredictably, often leading to catastrophic effects, it is important to understand which underlying control parameters are able to tune the failure behavior of materials and structures, including those that are heterogeneous and/or hierarchical. Improvements in the prediction of failure modes are essential to the design of optimal properties.Controlled studies of the brittle-ductile transition have been achieved both numerically and experimentally. For example, increasing material disorder has been shown [6-10] to increase the fracture process zone (FPZ) size, resulting in a less concentrated stress at the crick tip. The size of the FPZ eventually diverges for infinite disorder, producing a transition from a brittle narrow crack type failure to percolation-like diffuse behavior. Experimentally, Hanifpour et al. [11] showed that 3D-printed disordered auxetic lattices can fail in a ductile or brittle (with disorder-dependent tensile strength) manner depending on the loading direction. Driscoll et al. [12] demonstrated the key role of material rigidity in experiments on weakly-disordered honeycomb acrylic lattices, and also the key role of connectivity in numerical studies of two different types of spring networks, one of which was derived from numerical realizations of frictionless packings. Numerical studies in Zhang et al.[13], on the other hand, focused on how the nonlinear alignment of springs in a randomly diluted triangular lattice controls the transition at connectivities below what is known as the central force rigidity percolation point. Finally, Bouzid and Del Gado [14] focused on the role of connectivity in a disordered system, by studying the mechanical * corresponding author: Estelle Berthier (ehber...

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Network Topology in Soft Gels: Hardening and Softening Materials

Cited by 77 publications

References 64 publications

Correlated Rigidity Percolation and Colloidal Gels

Correlated Rigidity Percolation and Colloidal Gels

Computer simulations of colloidal gels: how hindered particle rotation affects structure and rheology

Rigidity percolation control of the brittle-ductile transition in disordered networks

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