Understanding physical aging in glasses is essential for technological applications as well as for fundamental research, since glasses are often considered as archetypes for systems far from thermodynamical equilibrium [1]. Notwithstanding, due to experimental limitations, no data directly probing the dynamics of realistic molecular glasses at a microscopic level are available so far. Here, we will report on the first experiments that follow at the atomic scale the relaxation and aging dynamics in a molecular glass former, a metallic melt, as the material gets frozen into a glass. Specifically, we show that the glass transition is accompanied by a dynamical crossover which leads to a complex hierarchy of aging behaviours in the glassy state [2]. These findings seem to be universal in structural glasses [3] and hold the promise to strongly improve the knowledge on the glassy state. In addition, we find clear similarities between our results in structural glasses and previous investigations on soft materials such as concentrated colloidal suspensions and polymeric gels [4]. Collectively, these findings suggest the notion of internal stress relaxation as a universal physical mechanism driving the dynamics of out of equilibrium materials. [1] P. G. Debenedetti & F. H. Stillinger, Nature 410 (2001) 259. [2] B. Ruta et al. Phys. Rev. Lett. 109 (2012) 165701. [3] B. Ruta et al. J. Chem. Phys. (2013) accepted. [4] L. Cipelletti, et al., Faraday Discuss. 123 (2003) 237.
Structural relaxation and aging in glasses studied by x-ray photon correlation spectroscopy
Baldi Giacomo;
2013
Abstract
Understanding physical aging in glasses is essential for technological applications as well as for fundamental research, since glasses are often considered as archetypes for systems far from thermodynamical equilibrium [1]. Notwithstanding, due to experimental limitations, no data directly probing the dynamics of realistic molecular glasses at a microscopic level are available so far. Here, we will report on the first experiments that follow at the atomic scale the relaxation and aging dynamics in a molecular glass former, a metallic melt, as the material gets frozen into a glass. Specifically, we show that the glass transition is accompanied by a dynamical crossover which leads to a complex hierarchy of aging behaviours in the glassy state [2]. These findings seem to be universal in structural glasses [3] and hold the promise to strongly improve the knowledge on the glassy state. In addition, we find clear similarities between our results in structural glasses and previous investigations on soft materials such as concentrated colloidal suspensions and polymeric gels [4]. Collectively, these findings suggest the notion of internal stress relaxation as a universal physical mechanism driving the dynamics of out of equilibrium materials. [1] P. G. Debenedetti & F. H. Stillinger, Nature 410 (2001) 259. [2] B. Ruta et al. Phys. Rev. Lett. 109 (2012) 165701. [3] B. Ruta et al. J. Chem. Phys. (2013) accepted. [4] L. Cipelletti, et al., Faraday Discuss. 123 (2003) 237.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
