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

摘要

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 alcohls 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 sise of alcohol and proximity to T_g. Close to the glas transition the variation of diffusion coefficient with temperature and composition does not follow that of viscosity and, for ethanol, diveragence was observed at T_g/T>0.88.