Universal Aging Features in the Restructuring of Fractal Colloidal Gels

We use multispeckle dynamic light scattering to measure the dynamic structure factor, f(q,τ), of gels formed by aggregation of colloids. Although the gel is an elastic solid, f(q,τ) nearly completely decays on long time scales, with an unusual form, f(q,τ)~exp-(τ/τf)^μ, with μ≈1.5 and with τf∝q^-1. A model for restructuring of the gel with aging correctly accounts for this behavior. Aging leads to a dramatic increase in τf; however, all data can be scaled on a single master curve, with τf 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.