Study of the relaxation behavior of a tri-epoxy compound in the supercoolde and glassy state by broadband dielectric spectroscopy

The dynamics of the glass-forming tri-epoxy triphenylolmethane triglycidyl ether (TPMTGE) was investigated in the supercooled and glassy state by broadband dielectric spectroscopy. Measurements were performed in a frequency range between 10(-2) Hz and 10(10) Hz for temperatures in the range between 120 and 350 K. The dielectric response revealed the existence of two relaxation processes: the lower frequency one (alpha -relaxation) slows down very rapidly on cooling the system and leaves the experimental window on approaching the glass transition temperature T-g; the higher frequency one (beta -relaxation) is observable both above and below T-g. The beta -relaxation is comparatively quite fast, thus a large separation between the main and the secondary peaks is observed, and no complete merging of the alpha- and the beta -process is found within the experimental window even at the highest temperatures. Besides, a third relaxation (beta '), very weak indeed, was observed in the glassy state. The detailed analysis performed on the experimental data indicated that a single Vogel-Fulcher-Tamman equation well describes the change of the alpha -relaxation time in the entire temperature interval. In the same temperature range, the conductivity and the alpha -relaxation time are related to each other by a fractional Debye-Stokes-Einstein law. Moreover, our results confirmed the proportionality between the beta -activation energy and the glass-transition temperature, which was found in other systems. As observed in previous experiments, both the shape parameters and the relaxation strength of beta -relaxation are strongly affected by the transition from liquid to glassy state.