Smart Energetic Nanosized Co-Crystals: Exploring Fast Structure Formation and Decomposition

The interest in co-crystals of energetic materials is explained by the fact that they can offer better thermodynamic stability and tunable sensitivity and detonation performance. In the present work, a combination of DSC, ultrafast chip calorimetry, high-resolution X-ray powder diffraction, and nanofocus X-ray diffraction was employed to investigate the thermal behavior and structure formation in nanosized co-crystals of CL-20 with HMX and TNT prepared using Spray Flash Evaporation (SFE). The CL-20/HMX cocrystal does not reveal any thermal transitions up to the thermal decomposition. In contrast, CL-20/TNT exhibits an irreversible melting transition. Upon melting, it can rapidly crystallize on heating or, at a slower pace, at room temperature to form homocrystals of gamma CL-20, the polymorph stable at high temperature. These observations constitute the first evidence of a CL-20 crystallization process, which occurs from the melt and not from solution. The solid-liquid phase separation occurring during heating CL-20-TNT melt may explain its complex thermal decomposition process as compared to that of CL-20/HMX: the main exothermic peak of decomposition can be assigned to that of a pure CL-20.