Crystal Structure Stability of CL-20/MTNP Energetic Cocrystals Without/with Polydopamine Coating in a Water/Organic Solvent Environment

Crystal structural stability is one of the core indicators for evaluating the safety of energetic materials, since these energetic materials undergo complex environments during manufacturing, processing, transportation, storage, and application in weapon systems. Energetic cocrystals are a novel solid form of energetic materials with unique crystal structures and novel properties. In this study, the crystal structure stability of hexanitrohexoazaisowurtzitane/1-methyl-3,4,5-trinitro-1H-pyrazole (CL-20/MTNP), an energetic cocrystal with high performance, in a water and organic solvent environment (acetone, N, N-dimethylacetamide, dimethyl sulfoxide and ethanol) is characterized. It was found that CL-20/MTNP partially decomposed and transformed to α-CL-20 both in pure water and a mixture of water and organic solvent, as confirmed by powder X-ray diffraction. The decomposition temperature of CL-20/MTNP and residual solid phase in a chemical environment were observed to be significantly different under thermal stimulation. The degree of the decomposition can be controlled by the temperature and soaking time. Unexpectedly, no significant changes were observed for the decomposition behavior after the introduction of organic solvents. Moreover, a polydopamine coating method was also applied to inhibit the decomposition of the cocrystal structure of CL-20/MTNP. These results are of significant reference value for understanding the crystal structure stability of energetic cocrystals and evaluating their safety in practical applications.