Qualitative change in structural dynamics of some glass-forming systems.

Analysis of the temperature dependence of the structural relaxation time τ(α)(T) in supercooled liquids revealed a qualitatively distinct feature-a sharp, cusplike maximum in the second derivative of logτ(α)(T)at some T(max). It suggests that the super-Arrhenius temperature dependence of τ(α)(T) in glass-forming liquids eventually crosses over to an Arrhenius behavior at T<T(max), and there is no divergence of τ(α)(T) at nonzero T. T(max) can be above or below T(g), depending on the sensitivity of τ(T) to a change in the liquid's density quantified by the exponent γ in the scaling τ(α)(T)∼exp(A/Tρ(-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.