Multispeckle x-ray photon correlation spectroscopy was employed to characterize the slow dynamics of a suspension of highly charged, nanometer-sized disks. At wave vectors $q$ corresponding to interparticle length scales, the dynamic structure factor follows a form $f(q,t)\sim \exp [-(t/\tau {)}^{\beta }]$, where $\beta \approx 1.5$. The relaxation time $\tau$ increases with the sample age $t_a$ approximately as $\tau \sim t_a^{1.8}$ and decreases with $q$ as $\tau \sim q^{-1}$. Such behavior is consistent with models that describe the dynamics in disordered elastic media in terms of strain from random, local structural rearrangements. The measured amplitude of $f(q,t)$ varies with $q$ in a manner that implies caged particle motion. The decrease in the range of this motion and an increase in suspension conductivity with increasing $t_a$ indicate a growth in interparticle repulsion as the mechanism for internal stress development implied by these models.

• Received 6 June 2004

DOI:https://doi.org/10.1103/PhysRevLett.93.228302