Variation in the Molecular Dynamics of DGEBA Confined within AAO Templates above and below the Glass-Transition Temperature

Abstract

In this paper, we have investigated the molecular dynamics above and below the glass-transition temperature of bisphenol-A diglycidyl ether (known as DGEBA, Mn = 340 g/mol) infiltrated in nanoporous alumina (AAO) templates of various pore sizes by means of dielectric and Raman spectroscopies. It was found that the temperature dependence of the structural relaxation times is different under confinement with respect to the bulk sample even in the high-temperature regime. Interestingly, below the glass-transition temperature, the slow secondary process (β) was not detected in dielectric loss spectra of confined DGEBA, while the relaxation times of the faster secondary process (γ) were unaffected by the pore size. To explain this phenomenon, two different scenarios, considering either suppression of the motions related to this mobility or enhancement of its dynamics, were taken into account. Additional annealing experiments, which lead to density perturbation, enabled us to recover bulk-like temperature dependence of structural relaxation times for all confined systems. This finding was discussed in view of the outcome of Raman and contact angle measurements that have shown rather weak interactions between DGEBA and the template. It is also worthwhile to add that except for the clear broadening of the fast secondary relaxation peak, the relaxation times of this process varied within experimental uncertainties due to annealing.