Comparative dielectric studies on two hydrogen-bonded and van der Waals liquids

Abstract

Broadband dielectric measurements were performed in a wide range of temperatures on glucose, maltose, and their acetyl derivatives. We have indicated that molecular dynamics above and below the glass transition temperature differ considerably for the hydrogen-bonded and van der Waals systems. We have shown that structural relaxation dispersions of D-glucose and maltose are broader than those obtained for peracetyl carbohydrates. Moreover, glass transition temperatures of the former systems are much higher than for the latter ones. In the glassy state of both glucose and its acetyl derivatives only one well-separated secondary relaxation process was identified. In the case of maltose and peracetyl maltose a completely different situation was observed. In the former carbohydrate two secondary modes were detected, whereas in the latter one only a faster relaxation process was visible in the glassy state. This finding is discussed in greater detail on the basis of density functional theory calculations.