Europhys. Lett.
Volume 76, Number 5, December 2006
Page(s) 972 - 978
Section Interdisciplinary physics and related areas of science and technology
Published online 01 November 2006
Europhys. Lett., 76 (5), pp. 972-978 (2006)
DOI: 10.1209/epl/i2006-10357-4

Length scale dependence of dynamical heterogeneity in a colloidal fractal gel

A. Duri and L. Cipelletti

Laboratoire des Colloïdes, verres et Nanomatériaux (UMR CNRS-UM2 5587) cc26, Université Montpellier 2 - 34095 Montpellier Cedex 5, France

received 11 September 2006; accepted 9 October 2006
published online 1 November 2006

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 $g_2(q,\tau)-1 \sim \exp[-(\tau/\tau_\mathrm{f})^p]$, with $\tau_\mathrm{f} \sim q^{-1}$ 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 $\chi(\tau,q)$ of the instantaneous autocorrelation function, the analogous of the dynamical susceptibility $\chi_4$ studied in glass formers. The amplitude of $\chi$ 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 $\chi$.

82.70.Dd - Colloids.
64.70.Pf - Glass transitions.
82.70.Gg - Gels and sols.

© EDP Sciences 2006