Diffusion in maltose-water mixtures at temperatures close to the glass transition

The mean diffusion coefficients, D, for maltose-water mixtures close to the glass transition temperature, Tg, 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 from 9.0 × 10−15 to 4.0 × 10−13 m2 s−1. The variation of D 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 Tg/T > 0.8.