Roles of Small Molecules in the Stability and Sensitivity of CL-20-Based Host–Guest Explosives under Electric Fields: A Reactive Molecular Dynamics Study

Host–guest inclusion, constructed by inserting small molecules into voids of energetic crystals, is a novel strategy for creating new energetic materials (EMs) with desired energy and safety. To provide an atomistic-level insight into the fact that small guest molecules can effectively regulate the stability and sensitivity of CL-20, we conducted ReaxFF-lg reactive molecular dynamics simulations on electric-field (EF)-induced decomposition of two typical host–guest EMs, CL-20/H₂O₂ and CL-20/N₂O, and compared it to that of α-CL-20 and ϵ-CL-20. Our findings show that the sensitivity order of the CL-20-based EMs under EFs, α-CL-20/H₂O₂ > ϵ-CL-20 > α-CL-20 > α-CL-20/N₂O, agrees well with the sensitivity obtained from the experiment (ϵ-CL-20 > α-CL-20 > α-CL-20/N₂O). Different effects of H₂O₂ and N₂O molecules were found responsible for the distinct stability and sensitivity of these materials toward EFs. On the one hand, H₂O₂ accelerate(s) the structural transformation of CL-20 and thus increases the sensitivity, because the wobbling NO₂ group reduces the stability of CL-20 by weakening its adjacent C–N bonds, whereas N₂O makes this transition less likely, resulting in low sensitivity of α-CL-20/N₂O. On the other hand, H₂O₂ and its decomposition intermediate OH radical can promote destruction of CL-20’s cage structure and produce a large amount of water molecules to release heat, making CL-20/H₂O₂ to decompose faster than ϵ-CL-20. N₂O molecules rarely react with CL-20 molecules but absorb heat from the surrounding decomposed CL-20 and thus slow down CL-20’s decomposition, resulting in low sensitivity of α-CL-20/N₂O, as confirmed by transition-state calculations. The results provide a comprehensive understanding of the stability and sensitivity of CL-20-based host–guest explosives under EFs.