A comparative study of the dielectric relaxation behaviour of glucose, maltose, and their mixtures with water in the liquid and glassy states

The dielectric relaxation behaviour of glucose, maltose, and their mixtures with water up to a concentration of 12.0 and 23.0% w/w, respectively, were examined in the frequency range 102 to 105Hz. A primary relaation was observed at temperatures above the glass transition temperature, Tg, and a secondary relaxation at sub-Tg temperatures. The addition of water shifted the primary relaxations to lower temperatures. For the glucose mixtures, water increased the strength of the secondary relaxation and resulted in a merging of the primary and secondary relaxations. The increase in strength of the secondary relaxation was much more marked for the maltose-water mixtures and, in this case, the relaxations remained separate over the range of frequency and water contents studied. For the maltose-water mixtures, the dependence of the strength of the secondary relaxation on the water content was bilinear with a change in gradient at ∼ 10.0% w/w water. The sub-Tg relaxations were thought to arise from motions of pendant hydroxymethyl groups attached to the hexose rings and from the reorientation of water molecules. The difference in the secondary relaxation behaviour of glucose and maltose indicates that structural factors, in addition to the presence of hydroxymethyl groups, are also important.