On the Stokes–Einstein relation in glass forming liquids

Abstract

Nowadays, the experimental evidence of a crossover between two dynamical regimes for supercooled glass-forming liquids at a temperature T c, T c>T g , where T g is the glass transition temperature, has been widely reported in the literature. On one hand, it is a well-known fact that in the region T g < T< T c , fragile glass forming liquids do not follow the Vogel–Fulcher–Tammann law. On the other hand, in the same region the Stokes–Einstein relation between the viscosity and the translational diffusion coefficient breaks down. Using the temperature derivative analysis, we present, for three glass-forming liquids, an empirical law for log 10 f , where f is the frequency, and we exhibit the break down of the Stokes–Einstein relation.