Departures from the correlation of time- and temperature-dependences of the alpha-relaxation in molecular glass-formers

摘要

There is a wel-known correlation beteen the spape of the relaxation function (nonexponentiality)and the temperataure-dependence of the relaxation times (e.g.,fragility),with broader relaxations associated with steeper T_g-normalized temperature dependences.Herein,exceptions ot this correlation are described.Five molecular glass-formers,all having very similar relaxation funcctions,are found to exhibit a arange of fragilities.,We slso show for two of these materials that,while pressure does not affect the breadth of the relaxation function,it substantially reduced the fragility.