Fluctations and noise in time-resolved light scattering experiments : measuring temporally heterogeneous dynamics

We use Time Resolved Correlation (TRC), a recently introduced light scattering method, to study the dynamics of a variety of jammed, or glassy, soft materials. The output of a TRC experiment is cI(t,tau), the time series of the degree of correlation between the speckle patterns generated by the light scattered at time t and t+tau. We characterize the fluctuations of cI by calculating their Probability Density Function, their variance as a function of the lag tau, and their time autocorrelation function. The comparison between these quantities for a Brownian sample and for jammed materials indicate unambiguously that the slow dynamics measured in soft glasses is temporally heterogeneous. The analogies with recent experimental, numerical and theoretical work on temporal heterogeneity in the glassy dynamics are briefly discussed.Comment: date de la fin de redaction : 06/09/200

Ultra-long range correlations of the dynamics of jammed soft matter

We use Photon Correlation Imaging, a recently introduced space-resolved dynamic light scattering method, to investigate the spatial correlation of the dynamics of a variety of jammed and glassy soft materials. Strikingly, we find that in deeply jammed soft materials spatial correlations of the dynamics are quite generally ultra-long ranged, extending up to the system size, orders of magnitude larger than any relevant structural length scale, such as the particle size, or the mesh size for colloidal gel systems. This has to be contrasted with the case of molecular, colloidal and granular ``supercooled'' fluids, where spatial correlations of the dynamics extend over a few particles at most. Our findings suggest that ultra long range spatial correlations in the dynamics of a system are directly related to the origin of elasticity. While solid-like systems with entropic elasticity exhibit very moderate correlations, systems with enthalpic elasticity exhibit ultra-long range correlations due to the effective transmission of strains throughout the contact network.Comment: To appear in Soft Matte

Spatial correlations and temporal heterogeneity of the slow dynamics of a colloidal fractal gel

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Dynamique lente et hétérogénéités temporelles dans un système micellaire concentré

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Dynamical heterogeneities in jammed systems

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Comment s'écoulent les poudres en réacteur ? Rhéophysique des milieux granulaires pour la maitrise des opérations unitaires de structuration, mélange et séparation

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Rhéophysique des milieux granulaires

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Heterogeneous dynamics: contribution of noise in TRC light scattering - going beyond TRC: space and time resolved light scattering

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Etude des hétérogénéités dynamiques dans la relaxation lente de la matière molle vitreuse

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Les hétérogénéités dynamiques dans la relaxation de la matière molle vitreuse

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