According to the elastic theory of the glass transition, the dynamics of glasses and glass-forming liquids are controlled by the evolution of shear modulus. In particular, the elastic shoving model expresses dynamics in terms of an activation energy required to shove aside the surrounding atoms, which is determined by the shear modulus. First, we here present an in situ high-temperature Brillouin spectroscopy test of the shoving model near the glass transition of eight aluminosilicate glass-forming systems. We find that the measured viscosity data agree qualitatively with the measured temperature dependence of shear moduli, as predicted by the shoving model. However, the model systematically underpredicts the values of fragility. Second, we also present a thorough test of the shoving model for predicting the low temperature dynamics of an aluminosilicate glass system. This is done by measuring the nonequilibrium viscosity over a wide range of fictive temperatures. We show that the model systematically underpredicts the changes in nonequilibrium viscosity with fictive temperature when compared with experimental data. Hence, both set of experiments suggest that the dynamics of the silicate glass transition are governed by additional factors beyond the evolution of the shear modulus.
Main Research Area:
7th International Discussion Meeting on Relaxations in Complex Systems, 2013