Relation between structural relaxation time and configurational entropy: A test of the Adam-Gibbs model on epoxy resins

Abstract

We compare the specific heat and dielectric relaxation (T) data of two epoxy resins, poly[(phenyl glycidyl ether)-co-formaldehyde] and diglycidyl ether of bisphenol A, with the predictions of the entropy theory of Adam and Gibbs. Specific heat data from temperature-modulated differential scanning calorimetry are used to evaluate configurational entropy S _C(T) data experimentally. The systems studied show two secondary (β and γ) relaxations inside the experimentally accessible frequency window of dielectric spectroscopy related to two crossover regions along the trace of the dynamic glass transition. The analysis, bypassing the use of the Vogel-Fulcher-Tamman equation, supports a good description of the structural relaxation time made in terms of the Adam-Gibbs model in the temperature range T _g < T < Tβ (or T _B), with Tβ the temperature where the structural and secondary β-relaxation times tend to merge, and T _B the temperature of deviation from a high-temperature Vogel-Fulcher-Tamman τ(T) dependence.