The nature of the gamma dielectric relaxation in diglycidyl ether Bisphenol-A (DGEBA) based epoxies

Abstract

A γ relaxation dielectric loss peak has been measured in the temperature range 113–163 K for a series of epoxy resins based on diglycidyl ether bisphenol-A (DGEBA). The network architecture of the examined systems were systematically altered using varied types of functional network modifiers featuring different functional groups. Analysis of the temperature dependence of the loss peak frequency leads to a radically new interpretation of the fundamental processes that are associated with the γ relaxation. The analysis has shown that the relaxation process can best be described in terms of a thermally assisted tunnelling displacement of a proton, termed activated tunnelling. The parameters derived not only fit the experimental data well, but have a clear physical origin that is shown to be consistent with the network topology as expressed through the glass transition temperature. The maximum temperature for which such behavior is observable has been determined and shown to be consistent with the measurements. The approach proposed here provides a new method for understanding γ relaxations in these and similar systems. Temperature T , dependence of the gamma relaxation frequency f p , for four related epoxy resin formulations. The curvature in the four data sets (◯ △ ▽ &square) is well reproduced by the activated tunnelling best fits (solid, long dash, short dash, dash dot lines), demonstrating that activated tunnelling is a better description than the traditional Arrhenius theory. • New physical understanding Gamma relaxations. • Thermally assisted proton tunnelling at local sites describes Gamma relaxation. • Activated tunnelling is a better description than the traditional Arrhenius theory. • Tunnelling parameters yield a description of the relaxation site potential surface. • Tunnelling parameters can be correlated with material topological constraints.