Hydrogen bonding in maltooligomer-glycerol-water matrices: Relation to physical state and molecular free volume

We use Fourier Transform Infra Red (FTIR) Spectroscopy to explore the effects of water and glycerol on the hydrogen bonding of low water content maltooligomer matrices by monitoring the shifts in the position of the peak associated with the fundamental stretching vibration of the hydroxyl groups, ν_OH. Changes in hydrogen bonding are investigated in relation to the physical state and the molecular packing of the maltooligomer matrices, which are measured by Positron Annihilation Lifetime Spectroscopy (PALS). In the concentration range studied (0-20 wt.%), glycerol acts as an anti-plasticizer whereby it reduces the average molecular hole size, v_h, while modulating the hydrogen bond network of the carbohydrate matrices. Depending on the level of hydration, water can cause anti-plasticization or plasticization of the maltooligomer-glycerol matrices. For water contents below ∼5 wt.%, water acts as an anti-plasticizer, whereby it reduces v_h and we measure a reduction ν_OH. At higher water contents, water acts as a plasticizer, causing a systematic increase in v_h, while ν_OH continues to decrease as a function of increasing water content.