Local motions in l-iditol glass: Identifying different types of secondary relaxations

The sub-Tg relaxations in amorphous l-iditol have been studied by thermally stimulated depolarisation currents (TSDC). The effect of aging on these motional processes was analysed during annealing at 253 and at 243 K, temperatures respectively 19 and 29 K below its calorimetric glass transition temperature Tg = 272 K. The features of different motional components of the secondary relaxation have been monitored as a function of time as the glass structurally relaxes on aging. It was concluded that the faster components of the secondary relaxation are negligibly dependent on aging and may be ascribed to intramolecular modes of motion, while the slower motional modes show a significant dependence on aging and correspond to the genuine Johari–Goldstein β-relaxation. The dielectric strength of the JG relaxation was found to decrease with increasing aging time, and there is no evidence for any modification with aging of the kinetic features of the local mobility.