Length scale dependence of dynamical heterogeneity in a colloidal fractal gelA. 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 , with 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 of the instantaneous autocorrelation function, the analogous of the dynamical susceptibility studied in glass formers. The amplitude of 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 .
82.70.Dd - Colloids.
64.70.Pf - Glass transitions.
82.70.Gg - Gels and sols.
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