Water and the glass transition temperature of organic (caramel) glasses

The glass transition temperature (Tg) of sugar-related glasses is close to room temperature and here we report the affect of water concentration on the Tg of caramel–water mixtures. Based on viscosity measurements, thermal analysis and X-ray diffraction (XRD) experiments we have investigated the occurrence of the Tg during differential scanning calorimetry (DSC) runs on cooling (down to ∼170 K) and heating cycles of the caramel glasses and caramel–water mixtures. The caramel–water mixtures are viscous melts with Newtonian rheology. Their melts bear a resemblance to a silicate melt which do not deviate from Vogel–Fulcher–Tammann (VFT) equation fit as the glass approaches Tg. The DSC measurements did detect low temperature transitions in caramel–water mixtures and the Tg of the dried caramel glass sample. If crystallization is avoided on cooling to ∼170 K then a glass transition and devitrification of the mixture will occur on heating the sample from ∼170 K up to the ambient room temperature. The detectability of the glass transition depends on the cooling rate and water concentration.