C,T-dependence of the Viscosity and the Self-diffusion Coefficients in Some Aqueous Carbohydrate Solutions

Self-diffusion coefficients for both components are reported for the highly concentrated aqueous solutions of some disaccharides and fructose as a function of temperature and concentration. These data are complemented by viscosity measurements. The disaccharides studied are sucrose, alpha,alpha-trehalose, allosucrose, and leucrose. Up to a sugar concentration of approximately 30% w/w the viscosity and the self diffusion coefficients of the four disaccharides are identical within experimental error for a given concentration and temperature. Water diffusion shows no differences in the four systems studied under these conditions. At higher concentrations significant differences are observed that become more pronounced with increasing temperature. Analysis of the data by the VTF equation yields the result that at a given concentration the self diffusion coefficients of the sugar Dc and the viscosity eta are described by identical ideal glass transition temperatures T0, while the diffusion of the water D(W) molecule decouples from these properties. T0(W) is always lower than T0(c,eta).