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

The relaxation behaviour of two molecular glass-forming systems, namely sor bitol and maltitol, are investigated in the large temperature range relevan t to the glass-transition. These data are obtained by combining three techn iques, 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)-10(7) s]. Two different relaxation processes can be observed. The princ ipal alpha-relaxation process exhibits a complex behaviour: comprising a no n-Arrhenius temperature dependence above T-g, (supercooled liquid state), a nd an Arrhenius behaviour below T-g (glassy state). A secondary beta-relaxa tion is observed at higher frequencies with an Arrhenius temperature depend ence. The secondary process appears in the same time-temperature range in b oth polyols. Consequently the molecular root of this relaxation is most lik ely the same in these complementary chemical systems. On the other hand, th e time scale on which the alpha and beta processes cross is very different for these two polyols. We relate this feature to the differences in the rel ative contributions of intra and inter-molecular interactions due to the di fferent chemical architecture of these polyols.