Relation between a transition in molecular mobility and collapse phenomenain glucose-water systems

In concentrated glucose glasses with water contents between 10 and 30 wt %, an indication for a transition in mobility of the sugar protons above the glass transition temperature is observed, using proton magnetic resonance t echniques. The first transition in mobility is positioned at the glass tran sition temperature while the second is about 20-30 degrees C higher. The te mperature of this second transition is found to depend on water content, re sulting in a new line in the state diagram of glucose-water mixtures. In fr eeze-concentrated glucose glasses we find two similar transitions. We inter pret the second transition as the so-called crossover temperature, where th e dynamics changes from solid-like to liquid-like. In freeze-concentrated g lasses an increase in the amount of ice melting per degree is observed just above the temperature of the second transition. We propose that both in co ncentrated and freeze-concentrated glucose glasses, this second transition relates to so-called collapse phenomena in glasses.