Interdependence of primary and Johari-Goldstein secondary relaxations in glass-forming systems.
We report evidence from broadband dielectric spectroscopy that the dynamics of the primary alpha- and secondary Johari-Goldstein (JG) beta-processes are strongly correlated in different glass-forming systems over a wide temperature T and pressure P range, in contrast with the widespread opinion of statistical independence of these processes. The alpha-beta mutual dependence is quantitatively confirmed by (a) the overall superposition of spectra measured at different T-P combinations but with an invariant alpha-relaxation time; (b) the contemporary scaling of the isothermal-pressure and isobaric-temperature dependences of the alpha-and beta-relaxation times as plotted versus the reduced variable Tg(P)/T where Tg is the glass transition temperature. These novel and model-independent evidences indicate the relevance of the JG relaxation phenomenon in glass transition, often overlooked by most current theories.
Kessairi
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Polylab CNR-INFM and Physics Department, Pisa University, Largo Pontecorvo 3, I-56127 Pisa, Italy.
Capaccioli
S
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Prevosto
D
D
Lucchesi
M
M
Sharifi
S
S
Rolla
P A
PA