TSDC in epoxy networks of well-controlled architecture: Experimental evidence for local and non-local relaxation process

Local and non-local relaxation processes were distinguished by investigating the heating rate dependence of the thermally stimulated discharge current (TSDC) line-shape in the case of three epoxy networks of well-controlled architecture. These networks were chosen because their chain dynamics differ by the relative extent of their local and short-scale cooperative molecular motions, as a consequence of marked differences in crosslink density. As far as local motions are concerned, the TSDC evolution measured at low temperature can be accounted for by using a model based on a distribution of activation energies. On the other hand, the higher temperature part of the spectrum of the densely crosslinked network, which mainly results from cooperative motions, shows a much different behavior which cannot be fitted by such a distribution model.