Fragility - Density of state and relaxation processes in polymeric materials

The values of diifferent parameters defined in the Random Walk Model (RWM) as: the Density of Possible Metastable States g(E), the metastable state Dumber N-E, the apparent activation energy E-a/R and, the Cooperative Rearranging Regions distribution sigma, have been calculated at T-g for two polymeric sample families (PVC, EVA(70), PVC/EVA(70) blend, and Unsaturated Polyester Resin samples). We show that these quantities allow to describe the configurational space, and we verify that the evolutions found for these different parameters versus the fragility are in a good agreement with the Strong-Fragile concept predictions. (c) 2006 Elsevier B.V. All rights reserved.