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 fun ction of temperature and concentration. These data are complemented by visc osity measurements. The disaccharides studied are sucrose, alpha,alpha-treh alose, allosucrose, and leucrose. Up to a sugar concentration of approximat e to 30% w/w the viscosity and the self diffusion coefficients of the four disaccharides are identical within experimental error for a given concentra tion and temperature. Water diffusion shows no differences in the four syst ems studied under these conditions. At higher concentrations significant di fferences are observed that become more pronounced with increasing temperat ure. Analysis of the data by the VTF equation yields the result that at a g iven concentration the self diffusion coefficients of the sugar D-c and the viscosity eta are described by identical ideal glass transition temperatur es T-0, while the diffusion of the water D-W molecule decouples from these properties. T-0(W) is always lower than T-0(c,eta). (C) 2000 Published by E lsevier Science Ltd. All rights reserved.