N ov 2 00 4 Off equilibrium fluctuations in a polymer glass . L . Buisson , S . Ciliberto

Off equilibrium fluctuations in a polymer glass. Abstract The fluctuation-dissipation relation (FDR) is measured on the dielectric properties a polymer glass (polycarbonate). It is observed that the fluctuation dissipation theorem is strongly violated for a quench from above to below the glass transition temperature. The amplitude and the persistence time of this violation are decreasing functions of frequency. Around 1Hz it may persist for several hours. The origin of this violation is a highly intermittent dynamics characterized by large fluctuations a strongly non-Gaussian statistics. The intermittent dynamics depends on the quenching rate and it disappears after slow quenches. The relevance of these results for recent models of aging are discussed. 1 Introduction Glasses are materials that play an important role in many industrial and natural processes. One of the most puzzling properties of these materials is the very slow relaxation towards equilibrium, named aging, that presents an interesting and unusual phenomenology. More specifically when a glassy system is quenched from above to below the glass transition temperature T g any response function of the material depends on the time t w elapsed from the quench[1]. For obvious reasons related to applications, aging has been mainly characterized by the study of the slow time evolution of response functions, such as the dielectric and elastic properties of these materials. It has been observed that these systems may present very complex effects, such as memory and rejuvenation[1, 2, 3, 4], in other words that their physical properties depend on the thermal history of the sample. Many models and theories have been constructed in order to explain the observed phenomenology, which is not yet completely understood. These models either predict or assume very different dynamical behaviours of the systems during aging. This dynamical behaviour can be directly related to 1