Effects of water content and molecular weight on spin probe and water mobility in malto-oligomer glasses

Spin probe rotational mobility has been studied by means of saturation tran sfer ESR in malto-oligomer-water glasses and has been compared to water mob ility as measured by H-1 NMR. Increasing the water content from 10 to 30 wt % leads to a decrease in spin probe mobility at T-g while the water mobili ty increases at T-g. From FTIR data we conclude that this decrease in spin probe mobility is caused by the fact that the overall packing of water and carbohydrate molecules in the hydrogen-bonded network becomes denser upon i ncreasing water content. From proton density measurements we conclude that the concomitant increase in mobility of water molecules is caused by the fa ct that the carbohydrate molecules become more separated from one another. Both water and spin probe mobility at T-g increase upon increasing the mole cular weight of the malto-oligomers (ranging from glucose up to maltoheptao se), while keeping the water content constant. This can be explained by the fact that larger oligomers form less densely packed networks.