In the last decades, a wide collection of experimental evidence was found in the study of supercooled glass-formers on the existence of a crossover between two dynamical regimes at a temperature Tc. The validity of the Vogel–Fulcher–Tammann model in both regions was considered. The breakdown in the Stokes–Einstein relationship below Tc was presented; indicating that the diffusion coefficient of a tracer became decoupled from the viscosity through an exponent, and the diffusion process was intensified. It was verified that a temperature shift of the diffusion coefficient introduced the same effect as the Stokes–Einstein breakdown equation. The dependence of this exponent upon the ratio between the radii of the tracer and the host liquid molecule was pointed out.

Tracer Diffusion in Glassforming Liquids. A.Andraca, P.Goldstein, L.F.del Castillo: Physica A, 2008, 387[18], 4531-40