Observation of liquid-crystal formation during melting of D-(+)-glucose

Liquid crystals, observed as maltese crosses under cross-polarized light, form in D-(+)-glucose immediately upon melting, at ～416 K, and become an isotropic liquid at ～500 K. Differential scanning calorimetry (DSC) results show two overlapping endothermic peaks corresponding to the formation and disappearance of the liquid crystals. Thermogravimetric analysis (TGA) confirmed that D-(+)-glucose undergoes thermal decomposition upon melting. Cooling and reheating isotropic samples previously heated to 500 K do not lead to the reappearance of the liquid crystals. The formation of liquid crystals is irreversible. Further study is required to determine which components among the decomposition intermediates or products of D-(+)-glucose are responsible for the formation of liquid crystals and whether they have process or product applications.