DIELECTRIC RELAXATIONS OF SMALL CARBOHYDRATE MOLECULES IN THE LIQUID AND GLASSY STATES

Dielectric permittivity and loss of a number of liquid and vitreous monosaccharides have been measured over a range of frequencies from 100 to 10(5) Hz and temperature range -100 to 150-degrees-C. In all cases either one or two relaxations were observed depending on the carbohydrate molecule; these occurred either just above the calorimetric T(g) in the case of a single relaxation or both above and below T(g) where two relaxations were observed. Fitting the relaxations to the Arrhenius equation, the sub-T(g) (or secondary) relaxation had an activation energy of approximately 45 kJ/mol in the two cases where it was observed. The primary relaxation activation energy varied from 177 to 353 kJ/mol depending on the monosaccharide. An explanation for the different values of activation energy is given in terms of the molecular structures of the monosaccharides, primary alcohol moieties conferring higher activation energies than those of similar molecules without primary alcohol groups. The lowest activation energies were observed for the noncyclic alditols xylitol and glucitol.