D. Pisignano et al., Study of the relaxation behaviour of a tri-epoxy compound in the supercooled and glassy state by broadband dielectric spectroscopy, J PHYS-COND, 13(20), 2001, pp. 4405-4419
The dynamics of the glass-forming tri-epoxy triphenylolmethane triglycidyl
ether (TPMTGE) was investigated in the supercooled and glassy state by broa
dband dielectric spectroscopy. Measurements were performed in a frequency r
ange 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 relaxa
tion processes: the lower frequency one (alpha -relaxation) slows down very
rapidly on cooling the system and leaves the experimental window on approa
ching the glass transition temperature T-g; the higher frequency one (beta
-relaxation) is observable both above and below T-g. The beta -relaxation i
s comparatively quite fast, thus a large separation between the main and th
e secondary peaks is observed, and no complete merging of the alpha- and th
e 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 experi
mental data indicated that a single Vogel-Fulcher-Tamman equation well desc
ribes the change of the alpha -relaxation time in the entire temperature in
terval. In the same temperature range, the conductivity and the alpha -rela
xation 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 paramet
ers and the relaxation strength of beta -relaxation are strongly affected b
y the transition from liquid to glassy state.