Glassforming Liquids, Amorphous and Semicrystalline Polymers: Exploring their Energy Landscape and Dynamical Heterogenei
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Applied Magnetic Resonance
REVIEW
Glassforming Liquids, Amorphous and Semicrystalline Polymers: Exploring their Energy Landscape and Dynamical Heterogeneity by Multi‑frequency High‑Field EPR Vasile Bercu1 · Carlo Andrea Massa2 · Silvia Pizzanelli2 · Luca Pardi2 · Dino Leporini2,3 · Massimo Martinelli4 Received: 12 June 2020 / Revised: 27 July 2020 © The Author(s) 2020
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. PACS 64.70.Pf · 76.30.-v · 61.25.Hq
1 Introduction Many disordered systems, 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]. However, the large variety of their local environments lead to wide distributions of both static and dynamical features of the paramagnetic * Dino Leporini [email protected] 1
Faculty of Physics, University of Bucharest, Str. Atomistilor 405, Magurele, Jud. Ilfov, Bucharest 077125, Romania
2
Istituto per i Processi Chimico-Fisici-Consiglio Nazionale delle Ricerche (IPCF-CNR), via G. Moruzzi 1, 56124 Pisa, Italy
3
Dipartimento di Fisica “Enrico Fermi”, Università di Pisa, Largo B. Pontecorvo 3, 56127 Pisa, Italy
4
Livorno, Italy
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centres with subsequent poor resolution of their EPR spectra. By employing higher and higher magnetic fields, these limitations have increasingly less impact and this aspect largely motivated the development of high-field electron paramagnetic (HFEPR) spectroscopy at W-band (95 GHz) or higher frequencies. Comprehensive textbooks [3], reviews [4], as well as concise introductions [5] concerning HF-EPR are available. Current applications of HF-EPR include studies concerning proteins and their model systems [3, 4], lipid membranes [4, 6], polymers [7]—e.g., the complex polymer lignin [8], conjugated polymers [9]—semiconductor nanocrystals [10], fullerenes [11], high-spin systems (S = 2) [12], and the development of new technologies for complex fluids [13]. The present paper reviews in a concise way the experimental efforts carried out in Pisa using the HF-EPR spectroscopy to provide novel insight into a wide class of disordered systems both in the solid state, i.e., amorphous polymers [14–20], and in the liquid state, i.e., glassforming viscous liquids [21, 22], polymer melts [21] and semicrystalline polymers [23, 24]. For completene
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