Low-temperature mobility of water in sugar glasses: Insights from thermally stimulated current study

Abstract

Molecular mobility in sucrose and sorbitol glasses, containing 35–1 % w/w water, is studied using thermally stimulating current method. Low-temperature dipole relaxation, Tgw, is observed in the temperature range of −125 to −155 °C and assigned to the rotational mobility of water molecules. From the concentration dependence of the Tgw, two regions are identified, i.e., intermediate water region (35–10 % w/w water), and low water region (less than 10 % w/w water). The results of this investigation, combined with earlier NMR (Girlich and Ludemann, Z Naturforsch 1994, 49c: 250) and neutron scattering (Chou et al, J Phys Chem B 2012, 116: 4439) studies, indicate that water molecules in sugar glasses form clusters at the intermediate water contents, whereas unclustered water molecules prevail at higher solute/lower water concentrations.