Aging behavior of Laponite clay particle suspensions

¹ Laboratoire de Dynamique des Fluides Complexes CNRS UMR 7506 Université Louis Pasteur - 3 rue de l'Université - 67084 Strasbourg, France
² Laboratoire de Physico-Chimie Macromoleculaire, CNRS UMR 7615, ESPCI 10 rue Vauquelin, 75231 Paris Cedex 5, France
³ Department of Chemical Engineering, Johns Hopkins University Baltimore, MD 21218, USA

Received: 20 April 2000
Accepted: 31 July 2000

Abstract

We use optical techniques to study the aging behavior of glassy colloidal suspensions of Laponite, a synthetic Hectorite clay. Multi-speckle diffusing wave spectroscopy measurements of tracer particle motion in Laponite suspensions show that the slow collective relaxation time τ of the glassy medium 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 particles in the terminal regime scales as , where . Light scattering studies of pure glassy Laponite suspensions show that the scattered light intensity is q-independent and decreases slowly with age, indicating that homogenization of the sample occurs during the aging process. We propose that the novel slow dynamics in this system is governed by random, localized stress relaxation events in the glassy phase.