A study of the deep structure of the energy landscape of glassy polystyrene: the exponential distribution of the energy-barriers revealed by high-field Electron Spin Resonance spectroscopy

TL;DR

This study uses high-field Electron Spin Resonance spectroscopy to reveal that the energy barriers for molecular reorientation in glassy polystyrene follow an exponential distribution, aligning with theoretical models of the energy landscape.

Contribution

It provides experimental evidence for the exponential distribution of energy barriers in glassy polystyrene using ESR spectroscopy, confirming theoretical predictions.

Findings

Exponential distribution of energy barriers observed at 240K and 270K.

Distribution shape consistent with previous mechanical and light scattering studies.

Energy barrier breadth matches estimates from other methods.

Abstract

The reorientation of one small paramagnetic molecule (spin probe) in glassy polystyrene (PS) is studied by high-field Electron Spin Resonance spectroscopy at two different Larmor frequencies (190 and 285 GHz). The exponential distribution of the energy-barriers for the rotational motion of the spin probe is unambigously evidenced at both 240K and 270K. The same shape for the distribution of the energy-barriers of PS was evidenced by the master curves provided by previous mechanical and light scattering studies. The breadth of the energy-barriers distribution of the spin probe is in the range of the estimates of the breadth of the PS energy-barriers distribution. The evidence that the deep structure of the energy landscape of PS exhibits the exponential shape of the energy-barriers distribution agrees with results from extreme-value statistics and the trap model by Bouchaud and coworkers.