Effects of water on the primary and secondary relaxation of xylitol and sorbitol: Implication on the origin of the Johari-Goldstein relaxation

Dielectric spectroscopy was employed to study the effects of water on the primary α-relaxation and the secondary β-relaxation of xylitol. The measurements were made on anhydrous xylitol and mixtures of xylitol with water with three different water concentrations over a temperature range from 1730.3em0exK to 2930.3em0exK. The α-relaxation speeds up with increasing concentration of water in xylitol, whereas the rate of the β-relaxation is essentially unchanged. Some systematic differences in the behavior of α-relaxation for anhydrous xylitol and the mixtures were observed. Our findings confirm all the observations of Nozaki et al. [R. Nozaki, H. Zenitani, A. Minoguchi, and K. Kitai, J. Non-Cryst. Solids 307, 349 (2002)] in sorbitol∕water mixtures. Effects of water on both the α- and β-relaxation dynamics in xylitol and sorbitol are explained by using the coupling model.