Beta relaxation versus high frequency wing in the dielectric spectra of a binary molecular glass former.
The binary molecular glass former 2-picoline in tri-styrene is investigated by means of broadband dielectric spectroscopy with the aim of understanding the role of secondary relaxation processes that emerge during the glass transition. It is shown that the "high frequency wing," which is seen in neat picoline, becomes a separate process in the mixture and exhibits all the features of a Johari-Goldstein relaxation. In particular, the previously found relation between activation energy and Tg is recovered. In addition, below Tg the width parameter of this secondary relaxation is shown to be governed by a common temperature dependence, and the time scale is characterized by an isokinetic point. Above Tg pronounced deviations from an Arrhenius behavior are observed.
Blochowicz
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TU-Darmstadt, 64289 Darmstadt, Germany.
Rössler
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EA