Abstract
We review past and recent work carried out on viscous liquids, amorphous and semicrystalline polymers by multifrequency high-field electron paramagnetic resonance (HF-EPR) facility in Pisa. The emphasis is on the enhanced ability to provide fine details of the reorientation process of the paramagnetic guest, the spin probe, revealing features driving the dynamics of the host system, including the energy-barrier distribution of glassy polymers, the dynamical heterogeneity of semicrystalline polymers, and the dynamical changes occurring at the critical temperature predicted by the ideal mode-coupling theory.
Highlights
Like glasses, liquids, polymers, and bio-systems, which are of interest in physics, materials science, biology, and chemistry, have been studied over the years by conventional X-band (9.5 GHz) electron paramagnetic resonance (EPR) spectroscopy [1, 2]
We have reviewed studies carried out by high-field electron paramagnetic resonance (HF-EPR) spectroscopy concerning amorphous polymers, glassforming viscous liquids, polymer melts, and semicrystalline polymers
They evidence that HF-EPR spectroscopy provides novel insight into two intensely investigated hallmarks of disordered systems, namely the topography of the energy landscape and the dynamical heterogeneity
Summary
Like glasses, liquids, polymers, and bio-systems, which are of interest in physics, materials science, biology, and chemistry, have been studied over the years by conventional X-band (9.5 GHz) electron paramagnetic resonance (EPR) spectroscopy [1, 2]. Two main issues were addressed, namely the distribution of energy barriers which must be overcome by the spin probe during the reorientation process [14,15,16,17,18,19,20] and the spatial distribution of microscopic mobility [23, 24] The former aspect is strictly related to the features of the so-called “energy landscape” of glasses, whereas the latter, dubbed “dynamical heterogeneity” [36, 37] is a distinctive feature of viscous liquids approaching the solidification process, known as glass transition, and is present in semicrystalline polymers due to coexistence of liquid and solid fractions.
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