title: Length scales and dynamics in the reorientational relaxation of tracers in molecular and polymeric glass formers via electron spin resonance spectroscopy.
abstract: It is widely accepted that a temperature region exists above the glass transition temperature, playing a fundamental role in the physics of polymers and glass formers. In this region, several dynamic crossovers have been experimentally and numerically revealed in the past years and the onset of glassy behavior is generally located, because of cooperative and heterogeneous features exhibited by the dynamics. In this Article, the rotational dynamics of two different stiff molecular spin probes dissolved in poly(propylene glycol) has been investigated by electron spin resonance spectroscopy in a wide temperature range. Decoupling phenomena between macroscopic and microscopic transport properties have been observed in the crossover region. A comparison with previous studies carried out with the same tracers dissolved in different polymers and glass formers strongly supports the idea that the observed crossover signals the onset of spatial correlations of dynamics on the length scale probed by the tracers.
authors.affiliation: Dipartimento di Fisica Enrico Fermi, Università di Pisa, Largo Bruno Pontecorvo 3, I-56127 Pisa, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Andreozzi
authors.forename: Massimo
authors.initials: M
authors.lastname: Faetti
authors.forename: Marco
authors.initials: M
authors.lastname: Giordano
authors.forename: Fabio
authors.initials: F
authors.lastname: Zulli