Direct imaging of contacts and forces in colloidal gels

Dong, Jun; Turci, Francesco; Jack, Robert L.; Faers, Malcolm A.; Royall, C. Patrick

doi:10.1063/5.0089276

Cited by 16 publications

(7 citation statements)

References 77 publications

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“…An important extension of this work would be a detailed comparison of our results with experiments, for example rheological studies [81] and confocal microscopy observations [68]. Finally, we note recent work where imaging has enabled forces between colloidal particles to be inferred, which could provide a direct comparison of the stress field [82].…”

Section: Discussionmentioning

confidence: 68%

Necking and failure of a colloidal gel arm: signatures of yielding on different length scales

Thijssen¹,

Liverpool²,

Royall³

et al. 2023

Preprint

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Colloidal gels consist of percolating networks of interconnected arms. Their mechanical properties depend on the individual arms, and on their collective behaviour. We use numerical simulations to pull on a single arm, built from a model colloidal gel-former with short-ranged attractive interactions. Under elongation, the arm breaks by a necking instability. We analyse this behaviour at three different length scales: a rheological continuum model of the whole arm; a microscopic analysis of the particle structure and dynamics; and the local stress tensor. Combining these different measurements gives a coherent picture of the necking and failure: the neck is characterised by plastic flow that occurs for stresses close to the arm's yield stress. The arm has an amorphous local structure and has large residual stresses from its initialisation. We find that neck formation is associated with increased plastic flow, a reduction in the stability of the local structure, and a reduction in the residual stresses; this indicates that the system loses its solid character and starts to behave more like a viscous fluid. We discuss the implications of these results for the modelling of gel dynamics.

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Section: Discussionmentioning

confidence: 68%

Necking and failure of a colloidal gel arm: signatures of yielding on different length scales

Thijssen¹,

Liverpool²,

Royall³

et al. 2023

Preprint

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“…Our results add to the body of sum rules in statistical mechanics [59][60][61][62] and they share formal similarities with sum rules for interface Hamiltonians [63], see [64] for recent work, and with the Takahashi-Ward identities [65,66] of quantum field theory. As locally resolved interparticle force measurements have been demonstrated in colloidal systems [67], future experimental use of the Noether force correlation functions looks feasible. Relating to forcesampling methods that reduce the statistical variance inherent in sampling results [68][69][70][71][72][73][74] is another interesting point for future work, as can be relating to force-based density functional theory [29,48].…”

Section: Discussionmentioning

confidence: 99%

Noether invariance theory for the equilibrium force structure of soft matter

Hermann,

Sammüller,

Schmidt

2024

J. Phys. A: Math. Theor.

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We give details and derivations for the Noether invariance theory that characterizes the spatial equilibrium structure of inhomogeneous classical many-body systems, as recently proposed and investigated for bulk systems [F. Sammüller et al., Phys. Rev. Lett. 130, 268203 (2023)]. Thereby an intrinsic thermal symmetry against a local shifting transformation on phase space is exploited on the basis of the Noether theorem for invariant variations. We consider the consequences of the shifting that emerge at second order in the displacement field that parameterizes the transformation. In a natural way the standard two-body density distribution is generated. Its second spatial derivative (Hessian) is thereby balanced by two further and different two-body correlation functions, which respectively introduce thermally averaged force correlations and force gradients in a systematic and microscopically sharp way into the framework. Separate exact self and distinct sum rules hold expressing this balance. We exemplify the validity of the theory on the basis of computer simulations for the Lennard-Jones gas, liquid, and crystal, the Weeks-Chandler-Andersen fluid, monatomic Molinero-Moore water at ambient conditions, a three-body-interacting colloidal gel former, the Yukawa and soft-sphere dipolar fluids, and for isotropic and nematic phases of Gay-Berne particles. We describe explicitly the derivation of the sum rules based on Noether's theorem and also give more elementary proofs based on partial phase space integration following Yvon's theorem.

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“…The forces between individual colloidal particles are also accessible experimentally [68]. It might therefore be possible to use force and torque sampling methods for the determination of distribution functions in experimental systems.…”

Section: Discussionmentioning

confidence: 99%

Reduced-variance orientational distribution functions from torque sampling

Renner

Schmidt

Heras

2023

J. Phys.: Condens. Matter

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We introduce a method to sample the orientational distribution function in computer simulations. The method is based on the exact torque balance equation for classical many-body systems of interacting anisotropic particles in equilibrium. Instead of the traditional counting of events, we reconstruct the orientational distribution function via an orientational integral of the torque acting on the particles. We test the torque sampling method in two- and three-dimensions, using both Langevin dynamics and overdamped Brownian dynamics, and with two interparticle interaction potentials. In all cases the torque sampling method produces profiles of the orientational distribution function with better accuracy than those obtained with the traditional counting method. The accuracy of the torque sampling method is independent of the bin size, and hence it is possible to resolve the orientational distribution function with arbitrarily small angular resolutions.

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Direct imaging of contacts and forces in colloidal gels

Cited by 16 publications

References 77 publications

Necking and failure of a colloidal gel arm: signatures of yielding on different length scales

Necking and failure of a colloidal gel arm: signatures of yielding on different length scales

Noether invariance theory for the equilibrium force structure of soft matter

Reduced-variance orientational distribution functions from torque sampling

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