DIFFUSION IN MALTOSE-WATER MIXTURES AT TEMPERATURES CLOSE TO THE GLASS-TRANSITION

The mean diffusion coefficients, (D) over bar, for maltose-water mixtures close to the glass transition temperature, T-g, were measured using a gravimetric method during desorption of water. The mass loss showed a linear dependence on the square root of time, indicating a Fickian diffusive process. At 300 K, an increase in the water content from 5.0 to 17.0% w/w resulted in an increase in (D) over bar from 9.0 X 10(-15) to 4.0 X 10(-13) m(2) s(-1). The variation of (D) over bar with temperature, at a water content of 9.5% w/w, yielded an activation energy of 70 kJ mol(-1). The variation of diffusion coefficient with temperature does not follow that of viscosity and diverges when T-g/T > 0.8.