Elucidating the structure–property relationships of CL-20/HMX energetic cocrystal materials based on molecular simulation

Abstract

2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20)–1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) cocrystal is one of the most promising energy-containing cocrystals. However, the formation mechanism of the CL-20-HMX cocrystal and its effect on the performance of the resulting product remain incompletely understood, which limits the practical application of the cocrystal explosives. In this study, the molecular mechanism of CL-20-HMX cocrystal formation was systematically investigated using density functional theory. The results revealed a substantial disparity in chemical potential between ε-CL-20 and β-HMX, indicating a strong tendency toward cocrystal formation. Moreover, abundant intermolecular interactions favor the formation of cocrystals. Molecular dynamics simulations were used to explore and explain the differences in mechanical and safety properties among cocrystals, mixture systems, and single components. The results indicate that, compared to CL-20, the CL-20-HMX cocrystal exhibits reduced rigidity, enhanced ductility, and improved safety properties.