The reorientation of the paramagnetic molecule TEMPO dissolved in glassy polystyrene (PS) is studied by high-field Electron Paramagnetic Resonance spectroscopy. Two different regimes separated by a crossover region are evidenced. Below 180 K the rotational times are nearly temperature independent with no apparent distribution. TEMPO is trapped. In the temperature range 180-220 K a large increase of the rotational mobility is observed with widening of the distribution of correlation times which exhibits two components: i) a delta-like, temperature-independent component representing the fraction of TEMPO w still trapped; ii) a strongly temperature-dependent component representing the fraction of untrapped TEMPO 1-w undergoing activated motion over an exponential distribution of barrier heights. Above 180 K a steep decrease of w is evidenced. The detrapping of TEMPO and the onset of its large increase of the rotational mobility at 180 K are interpreted as signatures of the onset of the fast motion detected by neutron scattering at T-f = 175 +/- 25 K.

The onset of the fast dynamics in glassy polystyrene observed by the detrapping of guest molecules: A high-field Electron Paramagnetic Resonance study

LEPORINI, DINO
2005-01-01

Abstract

The reorientation of the paramagnetic molecule TEMPO dissolved in glassy polystyrene (PS) is studied by high-field Electron Paramagnetic Resonance spectroscopy. Two different regimes separated by a crossover region are evidenced. Below 180 K the rotational times are nearly temperature independent with no apparent distribution. TEMPO is trapped. In the temperature range 180-220 K a large increase of the rotational mobility is observed with widening of the distribution of correlation times which exhibits two components: i) a delta-like, temperature-independent component representing the fraction of TEMPO w still trapped; ii) a strongly temperature-dependent component representing the fraction of untrapped TEMPO 1-w undergoing activated motion over an exponential distribution of barrier heights. Above 180 K a steep decrease of w is evidenced. The detrapping of TEMPO and the onset of its large increase of the rotational mobility at 180 K are interpreted as signatures of the onset of the fast motion detected by neutron scattering at T-f = 175 +/- 25 K.
2005
Bercu, V; Martinelli, M; Massa, Ca; Pardi, La; Leporini, Dino
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/99994
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