Fast equilibration mechanisms in disordered materials mediated by slow liquid dynamics*

The rate at which a nonequilibrium system decreases its free energy is commonly ascribed to molecular relaxation processes, arising from spontaneous rearrangements at the microscopic scale. While equilibration of liquids usually requires density fluctuations at timescales quickly diverging upon cooling, growing experimental evidence indicates the presence of a different, alternative pathway of weaker temperature dependence. Such equilibration processes exhibit a temperature-invariant activation energy, on the order of 100 kJ mol^-1.  We identify this molecular process with a slow relaxation mechanism, universally observed in the liquid dynamics of thin films. By adequately processing our samples, we have been able to enhance the nonequilibrium character and to detect a molecular process whose activation energy matches that of the equilibration rate. Our results show that measurements of liquid dynamics can be used to predict the equilibration rate in the glassy state