Onset of slow dynamics in difluorotetrachloroethane glassy crystal

TL;DR

This study combines experiments and simulations to analyze the reorientational dynamics of difluorotetrachloroethane glassy crystal, revealing a transition in rotational behavior and confirming Mode Coupling Theory predictions about static correlations and critical temperature.

Contribution

It provides new insights into the dynamic transition in glassy crystals and validates MCT scaling predictions for molecular reorientations.

Findings

Identification of a change in rotational dynamics at a specific temperature

Confirmation of MCT predictions for static correlations in glassy crystals

Determination of a critical temperature $T_c$ for the dynamic transition

Abstract

Complementary Neutron Spin Echo and X-ray experiments and Molecular Dynamics simulations have been performed on difluorotetrachloroethane (CFCl2-CFCl2) glassy crystal. Static, single-molecule reorientational dynamics and collective dynamics properties are investigated. The orientational disorder is characterized at different temperatures and a change in nature of rotational dynamics is observed. We show that dynamics can be described by some scaling predictions of the Mode Coupling Theory (MCT) and a critical temperature $T_{c}$ is determined. Our results also confirm the strong analogy between molecular liquids and plastic crystals for which $\alpha$-relaxation times and non-ergodicity parameters are controlled by the non trivial static correlations as predicted by MCT.