Diffusion of short chain alcohols from amorphous maltose-water mixtures above and below their glass transition temperature

The apparent diffusion coefficient for short chain alcohols in undercooled maltose-water mixtures close to the calorimetric glass transition temperature, T-g, was measured by following desorption using headspace gas chromatography. The plasticising effect of the alcohols on T-g was characterised using differential scanning calorimetry. The initial appearance of alcohol in the headspace showed a linear dependence on the square root of time, allowing it to be modelled as a Fickian diffusive process. The diffusion coefficient decreased with increasing molecular size of alcohol and proximity to T-g. Close to the glass transition the variation of diffusion coefficient with temperature and composition does not follow that of viscosity and, for ethanol, divergence was observed at T-g/T> 0.88. (C) 2000 Elsevier Science Ltd. All rights reserved.