Relaxation in the glass-former acetyl salicylic acid studied by deuteron magnetic resonance and dielectric spectroscopy

TL;DR

This study investigates the molecular relaxation processes in supercooled and glassy acetyl salicylic acid using dielectric spectroscopy and deuteron relaxometry, revealing deviations from typical behavior and characteristics of Johari-Goldstein relaxation.

Contribution

It provides new insights into the relaxation dynamics and energy barrier distributions in glassy acetyl salicylic acid through combined spectroscopic techniques.

Findings

Supercooled liquid shows deviations from thermally activated behavior.

Glass exhibits Johari-Goldstein secondary relaxation.

Large difference in activation energy between glass and crystalline form.

Abstract

Supercooled liquid and glassy acetyl salicylic acid was studied using dielectric spectroscopy and deuteron relaxometry in a wide temperature range. The supercooled liquid is characterized by major deviations from thermally activated behavior. In the glass the secondary relaxation exhibits the typical features of a Johari-Goldstein process. Via measurements of spin-lattice relaxation times the selectively deuterated methyl group was used as a sensitive probe of its local environments. There is a large difference in the mean activation energy in the glass with respect to that in crystalline acetyl salicylic acid. This can be understood by taking into account the broad energy barrier distribution in the glass.