Length scale dependence of dynamical heterogeneity in a colloidal fractal gel

Agnes Duri; Luca Cipelletti

doi:10.1209/epl/i2006-10357-4

paper

Length scale dependence of dynamical heterogeneity in a colloidal fractal gel

arXiv:cond-mat/0606051 · doi:10.1209/epl/i2006-10357-4

Abstract

We use time-resolved dynamic light scattering to investigate the slow dynamics of a colloidal gel. The final decay of the average intensity autocorrelation function is well described by $g_2 (q, τ) - 1 \sim exp [- (τ / τ_f)^{p}]$ , with $τ_f \sim q^{- 1}$ and $p$ decreasing from 1.5 to 1 with increasing $q$ . We show that the dynamics is not due to a continuous ballistic process, as proposed in previous works, but rather to rare, intermittent rearrangements. We quantify the dynamical fluctuations resulting from intermittency by means of the variance $χ (τ, q)$ of the instantaneous autocorrelation function, the analogous of the dynamical susceptibility $χ_4$ studied in glass formers. The amplitude of $χ$ is found to grow linearly with $q$ . We propose a simple --yet general-- model of intermittent dynamics that accounts for the $q$ dependence of both the average correlation functions and $χ$ .

Revised and improved, to appear in Europhys. Lett

Length scale dependence of dynamical heterogeneity in a colloidal fractal gel

Abstract

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