Aging behavior of Laponite clay particle suspensions

We use optical techniques to study the aging behavior of glassy colloidal s uspensions of Laponite, a synthetic Hectorite clay. Multi-speckle diffusing wave spectroscopy measurements of tracer particle motion in Laponite suspe nsions show that the slow collective relaxation time tau of the glassy medi um scales linearly with the age t(w) of the sample, a universal feature of many glassy systems. Moreover, the mean-square displacement of the tracer p articles in the terminal regime scales as [Delta r(2)(t(w), t)] similar to (t/t(w))(gamma), where gamma = 1.5 +/- 0.1. Light scattering studies of pur e glassy Laponite suspensions show that the scattered light intensity is q- independent and decreases slowly with age, indicating that homogenization o f the sample occurs during the aging process. Wt propose that the novel slo w dynamics in this system is governed by random, localized stress relaxatio n events in the glassy phase.