Dynamics and cooperativity in thermoset networks by dielectric relaxation spectroscopy

Dipole dynamics in the network-forming epoxy-amine formulations were investigated by dielectric relaxation spectroscopy. Frequency sweeps were performed on the neat and the solvent-containing networks at various stages of cure and the activation energy for the ex process, the width and the shape of the relaxation spectrum, and the intermolecular cooperativity were analyzed. An explanation for the changes in activation energy is offered in terms of the formation and break-up of hydrogen-bonded complexes near the gel point. Fits to the KWW expression could be obtained for the neat formulation but not for the solvent-containing formulation. In the former case, the KWW parameter, β, decreased linearly with the degree of cure. An explanation of the relative contributions of differing mobility scales to the network dynamics at various stages of cure was also attempted in terms of a power-law model. Finally, the fragility or cooperativity plots proved informative in relating intermolecular cooperativity to the molecular characteristics of a network.