Length scale dependence of dynamical heterogeneity in a colloidal fractal gel

Agnes Duri (1) , Luca Cipelletti (1)

1 LCVN - Laboratoire des colloïdes, verres et nanomatériaux

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 $\chi$.

Mots clés: glassy dynamics; dynamical heterogeneity; gel; colloids; light scattering

Domaines: Matière Molle [cond-mat.soft]

Agnes Duri, Luca Cipelletti. Length scale dependence of dynamical heterogeneity in a colloidal fractal gel. EPL - Europhysics Letters, 2006, 76 (5), pp.972. ⟨10.1209/epl/i2006-10357-4⟩. ⟨hal-00078005v2⟩