Dynamics of sorbitol and maltitol over a wide time-temperature range

Abstract:

The relaxation behaviour of two molecular glass-forming systems, namely sorbitol and maltitol, are investigated in the large temperature range relevant to the glass-transition. These data are obtained by combining three techniques, i.e. low-frequency mechanical spectroscopy, medium and high frequency dielectric spectroscopy, and viscosity measurements. This procedure allows to determine the relaxation map of these polyols on a wide time range [10^-9-10⁷ s]. Two different relaxation processes can be observed. The principal α-relaxation process exhibits a complex behaviour, comprising a non-Arrhenius temperature dependence above T _g (supercooled liquid state), and an Arrhenius behaviour below T _g (glassy state). A secondary β-relaxation is observed at higher frequencies with an Arrhenius temperature dependence. The secondary process appears in the same time-temperature range in both polyols. Consequently the molecular root of this relaxation is most likely the same in these complementary chemical systems. On the other hand, the time scale on which the α and β processes cross is very different for these two polyols. We relate this feature to the differences in the relative contributions of intra and inter-molecular interactions due to the different chemical architecture of these polyols.