Dynamics of sugar solutions as studied by dielectric spectroscopy

We present dielectric and calorimetric results on solutions of glucose, fructose and sucrose over wide frequency and temperature ranges. For all the samples the dielectric data exhibits two clear relaxation processes with different temperature dependences. We provide support for the interpretation that the faster one, with an Arrhenius temperature dependence of its relaxation time, is mainly due to a local beta-relaxation of the hydration water, whereas the slower one, with a non-Arrhenius temperature dependence, corresponds to the cooperative alpha-relaxation of the hydrated sugar molecules. The latter process is directly coupled to the viscosity of the system and its relaxation time decreases rapidly with increasing water content due to the plasticizing effect of the bound water, in accordance with the rapid decrease of the calorimetric glass transition temperature. The results support recent findings that most mixtures of water and other molecules breaks up the hydrogen bonded network of supercooled water, leading to that a Gordon-Taylor fit to the glass transition temperatures at different hydration levels does not extrapolate to the glass transition temperature of bulk water, but rather to the temperature where the above mentioned P-relaxation of the water freezes in. (c) 2005 Elsevier B.V. All rights reserved.