Formation of molecular alloy by solid-state amorphisation
Satoshi Furukawa, Maki Nagahama, Hiroshi Suga
Deoxycholic acid (DCA) crystal was found to be amorphised easily by mechanical grinding at room temperature. X-ray and differential scanning calorimetry (DSC) experiments showed a glass transition, crystallisation, and subsequent fusion processes characteristic of a vitreous solid. A mixture of DCA and tri-O-methyl-b-cyclodextrin (TMCD) crystals also gave a halo pattern in the x-ray experiment after grinding. The DSC curve exhibited only a single glass transition in the vitrified binary solid. This indicates that the molecules of DCA and TMCD were mixed on a microscopic level, which yields a single structural relaxation in the vitreous solid. The devitrified solid gave double fusion processes, indicating a phase separation at the devitrification temperature. Thus, the formation of a molecular alloy was possible only under nonequilibrium conditions. Glucose which could not be amorphised by itself was forced to be vitrified by coexistence with TMCD crystal. The formation of molecular alloy was discussed in relation to the disorder of the systems.