Qualitative change in structural dynamics of some glass-forming systems

Abstract

Analysis of the temperature dependence of the structural relaxation time τα(T ) in supercooled liquids revealed a qualitatively distinct feature—a sharp, cusplike maximum in the second derivative of logτα(T )at some Tmax. It suggests that the super-Arrhenius temperature dependence of τα(T ) in glass-forming liquids eventually crosses over to an Arrhenius behavior atT <Tmax, and there is no divergence of τα(T ) at nonzero T . Tmax can be above or below Tg, depending on the sensitivity of τ (T ) to a change in the liquid’s density quantified by the exponent γ in the scaling τα(T ) ∼ exp(A/T ρ −γ ). These results might turn the discussion of the glass transition in a different direction—toward the origin of the limiting activation energy for structural relaxation at low T .