Universal Aging Features in the Restructuring of Fractal Colloidal Gels

We use multispeckle dynamic light scattering to measure the dynamic structure factor, $f(q,\tau )$, of gels formed by aggregation of colloids. Although the gel is an elastic solid, $f(q,\tau )$ nearly completely decays on long time scales, with an unusual form, $f(q,\tau )\sim \exp \{-(\tau /{\tau }_f{)}^{\mu }\}$, with $\mu \approx 1.5$ and with ${\tau }_f\propto q^{-1\mathrm{}}$. A model for restructuring of the gel with aging correctly accounts for this behavior. Aging leads to a dramatic increase in ${\tau }_f$; however, all data can be scaled on a single master curve, with ${\tau }_f$ asymptotically growing linearly with age. This behavior is strikingly similar to that predicted for aging in disordered glassy systems, offering convincing proof of the universality of these concepts.