Résumé:

We investigate the slow dynamics of a soft glass, a concentrated suspension of polydisperse colloidal particles, by using multispeckle Diffusing Wave Spectroscopy (DWS). Two distinct regimes are observed: for small sample age, t(w), the dynamics smoothly slows down, as revealed by a nearly linear increase of the characteristic relaxation time, tau(s), measured by DWS. At longer ages, the dynamics is quasi stationary, but tau(s) exhibit anomalously large fluctuations in time. The time scale of the dynamical fluctuations is found to be slightly shorter than the average relaxation time. The variance of the intensity correlation function is maximum for time delays comparable to the average relaxation time, in striking analogy with recent simulations of glass-forming liquids.