Accumulating evidence for non-diverging time-scales in glass-forming fluids

One perceived important signature of the ideal glass transition and of the complex fluid nature of glass-forming liquids remains the apparent divergence of the dynamics at temperatures above zero Kelvin. Recently, however, this perception has been increasingly challenged both through experiment, large scale data analysis, and in some new theories of the dynamics of glass forming systems. Here we summarize early evidence suggesting that time scales actually do not diverge in glasses that are aged into equilibrium, perhaps 15 degrees C below the conventional glass transition temperature T-g. We then show novel results from an extremely densified glass - 20 million year old Dominican amber - in which we were able to obtain the upper bounds to the relaxation times at temperatures below the glass transition temperature through a step-wise temperature scan in which the stress relaxation response of the amber was measured both below and above the fictive temperature T-f. We find that in the case of the upper bound responses at T > T-f, there is a strong deviation of the response from the Super-Arrhenius Vogel-Fulcher-Tammann (VFT) extrapolation and this persists to the fictive temperature which is some 43.6 degrees C below T-g. Evidence is also presented suggesting that different dynamic properties may deviate from the VFT extrapolation differently and challenges for future measurement are presented. (C) 2014 Elsevier B.V. All rights reserved.