It was recalled that colloidal dispersions of Laponite platelets were known to age slowly, from viscous sols to colloidal glasses. This aging process was followed by monitoring the diffusion of probe particles, embedded in the sample, by dynamic light-scattering. The results showed that time-dependent diffusion of the probe particles scaled with their size in early stages and for larger particles. This implied that, within this regime, the measurements could be used to investigate the generalized fluctuation-dissipation theorem for the out-of-equilibrium system, where the bath temperature was replaced by an effective temperature. Simultaneous dynamic rheological measurements revealed that this effective temperature increased as a function of aging time and frequency. This suggested the existence of 2 measured time-scale regimes. In accord with recent work, the present results suggested that, at probed time-scales longer than the characteristic relaxation time of the Laponite dispersion, the system thermalized with the bath. At shorter time-scales, the system was out-of-equilibrium; with an effective temperature that was greater than the bath temperature.

Size-Dependent Diffusion in an Aging Colloidal Glass. D.R.Strachan, G.C.Kalur, S.R.Raghavan: Physical Review E, 2006, 73[4], 041509 (5pp)