M. Jiménez-Ruiz

Rotational freezing in plastic crystals: a model system for investigating the dynamics of the glass transition

The dynamics of the rotational freezing transition of the rotator phase (RP) crystal of ethanol into its orientational glass (OG) phase is monitored by measurements of molecular rotational components in the quasielastic neutron scattering spectrum. Such a transition is known to share several features in common with the canonical liquid glass transition (both taking place within the same temperature interval), and therefore some of the results from such a study should be of relevance for our understanding of the latter. We show that the basic features of the RP OG transition can be understood in terms of a hard-needle model by means of a mapping of the aspect ratio onto a temperature scale.

Glassy dynamics of a kinetically constrained model: a direct comparison with experiment

The dynamics of the freezing transition of the rotator-phase crystal of ethanol into its orientational glass phase is monitored by measurements of molecular rotational components in the quasielastic neutron scattering spectrum. It is shown that phenomena experimentally observed at pico- and nanosecond scales can be mapped onto those shown by a model of infinitely thin hard needles rotating about body-centred cubic lattice positions. The basic signatures that appear on crossing the orientational glass transition are similar in the needle model and in the neutron scattering data for ethanol. As the model glass transition is of purely dynamical origin, our findings support the idea that the glass transition is purely dynamical and is not associated with an underlying thermodynamic phase transition.