Resolving Long-Range Spatial Correlations in Jammed Colloidal Systems Using Photon Correlation Imaging

Duri, Agnès; Sessoms, David A.; Trappe, Véronique; Cipelletti, Luca

doi:10.1103/physrevlett.102.085702

Cited by 95 publications

(148 citation statements)

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“…At large q, corresponding to in-cage motion, we find diffusive dynamics τ ∼ q −2 accompanied by stretched exponential relaxations, β < 1. At larger lengthscales, a crossover to nearly ballistic dynamics τ ∼ q −1 is accompanied by compressed exponential β > 1 with a peak value near β ≈ 1.5 as frequently reported in experiments [23,27]. Eventually, diffusive dynamics and exponential relaxation should be recovered at large enough lengthscales, but these are difficult to access within our numerical simulations.…”

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confidence: 88%

“…In addition, compressed exponentials are seen to emerge only for large enough displacements, with the relaxation timescale τ (q) crossing over from τ ∼ q −2 , characteristics of diffusion, to τ ∼ q −1 , characteristic of ballistic dynamics, with decreasing the scattering wavevector q. Finally, spatiallyresolved dynamic measurements revealed the existence of long-ranged correlations extending up to the system size [27,28], again contrasting with the much smaller-ranged dynamic heterogeneity observed in glassy materials [29]. Such peculiar behaviour is hypothesized to follow from the infrequent release of 'internal stresses' that relax the fractal network [18], but this interpretation remains to be confirmed by direct observation.…”

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confidence: 98%

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Ultra-long-range dynamic correlations in a microscopic model for aging gels

Chaudhuri

Berthier

2017

Phys. Rev. E

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We use large-scale computer simulations to explore the nonequilibrium aging dynamics in a microscopic model for colloidal gels. We find that gelation resulting from a kinetically-arrested phase separation is accompanied by 'anomalous' particle dynamics revealed by superdiffusive particle motion and compressed exponential relaxation of time correlation functions. Spatio-temporal analysis of the dynamics reveals intermittent heterogeneities producing spatial correlations over extremely large length scales. Our study is the first microscopically-resolved model reproducing all features of the spontaneous aging dynamics observed experimentally in soft materials.Understanding the complex mechanisms underlying the formation and stability of colloidal gels remains a challenge, despite the diversity of existing applications exploiting their mechanical properties. Gels are lowdensity structures forming percolating networks, with bonds that are either permanent (chemical gels) or transient (physical gels) [1][2][3][4][5][6]. A prevalent method to form physical gels follows a nonequilibrium route by quenching a homogeneous fluid into a phase coexistence region [1,[7][8][9][10][11][12], which generates bicontinuous structures. When the dense phase forms an amorphous solid, the phase separation is kinetically hindered [13][14][15][16] and a gel forms. The microscopic dynamical and structural properties of these nonequilibrium gels evolve slowly with time.This aging dynamics has been the subject of many experimental studies, which established that aging in colloidal gels is 'anomalous' [17,18], i.e. it differs qualitatively from the aging observed in conventional glassy materials, such as polymer and colloidal glasses [19,20]. Scattering experiments [21][22][23][24][25] report that time correlation functions are described by compressed exponential relaxations. Such behaviour differs from the (exponential) diffusive dynamics in simple liquids or the (stretched exponential) decay observed in glassy fluids [26]. In addition, compressed exponentials are seen to emerge only for large enough displacements, with the relaxation timescale τ (q) crossing over from τ ∼ q −2 , characteristics of diffusion, to τ ∼ q −1 , characteristic of ballistic dynamics, with decreasing the scattering wavevector q. Finally, spatiallyresolved dynamic measurements revealed the existence of long-ranged correlations extending up to the system size [27,28], again contrasting with the much smaller-ranged dynamic heterogeneity observed in glassy materials [29]. Such peculiar behaviour is hypothesized to follow from the infrequent release of 'internal stresses' that relax the fractal network [18], but this interpretation remains to be confirmed by direct observation. This overall phenomenology has been reported for laponite, carbon black, micellar polycrystals, multilamellar vesicles, implying it is generic to a large class of soft materials [18].A microscopic perspective via theoretical modeling is also missing. To study this problem, one needs a model with a...

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confidence: 88%

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confidence: 98%

Ultra-long-range dynamic correlations in a microscopic model for aging gels

Chaudhuri

Berthier

2017

Phys. Rev. E

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“…that it is faster in some regions and slower in others [2][3][4]. Direct microscopic evidence for this behavior has been found both in simulations [4,5] and in experiments [4,[6][7][8][9][10][11][12][13][14][15][16]. The understanding of dynamical heterogeneity is believed to be crucial to explain anomalous behavior of materials near the glass transition, and even possibly to explain the very presence of the glass transition itself [2].…”

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confidence: 99%

Fluctuations in the time variable and dynamical heterogeneity in glass-forming systems

2013

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We test a hypothesis for the origin of dynamical heterogeneity in slowly relaxing systems, namely that it emerges from soft (Goldstone) modes associated with a broken continuous symmetry under time reparametrizations. We do this by constructing coarse grained observables and decomposing the fluctuations of these observables into transverse components, which are associated with the postulated time-fluctuation soft modes, and a longitudinal component, which represents the rest of the fluctuations. Our test is performed on data obtained in simulations of four models of structural glasses. As the hypothesis predicts, we find that the time reparametrization fluctuations become increasingly dominant as temperature is lowered and timescales are increased. More specifically, the ratio between the strengths of the transverse fluctuations and the longitudinal fluctuations grows as a function of the dynamical susceptibility, χ4, which represents the strength of the dynamical heterogeneity; and the correlation volumes for the transverse fluctuations are approximately proportional to those for the dynamical heterogeneity, while the correlation volumes for the longitudinal fluctuations remain small and approximately constant.

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“…The particles have an intrinsic optical anisotropy; accordingly, they scatter light with polarization both parallel and perpendicular ("depolarized") to that of the incident radiation. The depolarized scattered intensity is an accurate probe of the local particle concentration [16].To probe the sedimentation process in great detail, we use a custom-designed light scattering apparatus [19], sketched in Fig. SM1 [18].…”

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Highly Nonlinear Dynamics in a Slowly Sedimenting Colloidal Gel

et al. 2011

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We use a combination of original light scattering techniques and particles with unique optical properties to investigate the behavior of suspensions of attractive colloids under gravitational stress, following over time the concentration profile, the velocity profile, and the microscopic dynamics. During the compression regime, the sedimentation velocity grows nearly linearly with height, implying that the gel settling may be fully described by a (time-dependent) strain rate. We find that the microscopic dynamics exhibit remarkable scaling properties when time is normalized by strain rate, showing that the gel microscopic restructuring is dominated by its macroscopic deformation.PACS numbers: 47.57.ef, 64.70.pv, 82.70.Dd Gels and attractive glasses resulting from the aggregation of colloidal particles are the subject of extensive studies because their physical behavior often results from a complex interplay between equilibrium thermodynamics and nonequibrium dynamic processes [1][2][3], and because they are relevant for understanding networkforming biological systems [4] and for industrial applications. Although they exhibit solid-like mechanical properties, colloidal gels are easily disrupted by small perturbations, such as gravitational forces. While a large body of macroscopic observations of gels under gravitational stress exists [5][6][7][8][9][10][11][12][13], very little is known on the microscopic processes at play during sedimentation, thus limiting our ability to understand and predict the behavior of sedimenting gels.Here, we use a novel light scattering method to gain access to the dynamics of a slowly settling colloidal system from the macroscopic deformation of the sample down to the relaxational behavior at the particle scale. We find that the very slow macroscopic deformation occurs via irreversible plastic events at the microscopic scale. Remarkably, the gel behavior at all scales is controlled by a single parameter, the time-dependent compression rate, in striking analogy with recent observations on deformed polymer [14] and colloidal [15] glasses.We study gels formed by attractive colloidal hard spheres with radius R = 82 ± 3 nm, suspended in an aqueous solvent at an initial volume fraction ϕ 0 = 0.123 (more details can be found in [16][17][18]). Gelation is induced by attractive depletion forces obtained by adding micelles of a nonionic surfactant. The interaction between colloids is well described by the Asakura-Oosawa depletion potential [16], with a range r ≈ 3 nm. The potential can be mapped on the Adhesive Hard Sphere model, with a stickiness parameter τ ≃ 0.01 [16,17]. The density mismatch between the particles and the solvent is ∆ρ = 1.12 g/cm 3 . The particles have an intrinsic optical anisotropy; accordingly, they scatter light with polarization both parallel and perpendicular ("depolarized") to that of the incident radiation. The depolarized scattered intensity is an accurate probe of the local particle concentration [16].To probe the sedimentation process in great detail, we use...

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Resolving Long-Range Spatial Correlations in Jammed Colloidal Systems Using Photon Correlation Imaging

Cited by 95 publications

References 23 publications

Ultra-long-range dynamic correlations in a microscopic model for aging gels

Ultra-long-range dynamic correlations in a microscopic model for aging gels

Fluctuations in the time variable and dynamical heterogeneity in glass-forming systems

Highly Nonlinear Dynamics in a Slowly Sedimenting Colloidal Gel

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