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

JD Zhang and W Guo, JOURNAL OF PHYSICAL CHEMISTRY A, 126, 286-295 (2022).

DOI: 10.1021/acs.jpca.1c09409

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 electricfield (EF)-induced decomposition of two typical host-guest EMs, CL-20/H2O2 and CL-20/N2O, and compared it to that of alpha-CL-20 and epsilon-CL-20. Our findings show that the sensitivity order of the CL-20-based EMs under EFs, alpha-CL-20/H2O2 > epsilon-CL-20 > alpha- CL-20 > alpha-CL-20/N2O, agrees well with the sensitivity obtained from the experiment (epsilon-CL-20 > alpha-CL-20 > alpha-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 alpha-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 epsilon-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 alpha-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.

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