Chemical Insight on Decreased Sensitivity of CL-20/TNT Cocrystal Revealed by ReaxFF MD Simulations

Understanding the underlying mechanisms on sensitivity-decrease of the CL-20/TNT cocrystal is essential for wide applications of the promising high-energetic CL-20. This work presents the chemical scenario of CL-20/TNT thermolysis obtained from ReaxFF molecular dynamics simulations. Facilitated by the unique VARxMD for reaction analysis, the interplay reactions between CL-20 and TNT responsible for the sensitivity-decrease of CL-20/TNT was first revealed. The early response of CL-20/TNT to thermal stimulus is dominated by N-NO₂ bond cleavage for NO₂ formation and C-N bond scission leading to ring-opening of CL-20. The kinetics of N-NO₂ and C-N bond cleavage, as well as the following oxygen-abstraction of NO₂, are significantly slowed in the CL-20/TNT thermolysis against β-CL-20, which are responsible for the low sensitivity at the stage of active intermediate generation. The early formed active intermediates of NO₂, NO₃, NO, and N₂O are confined and consumed by the reactions of the surrounding TNT or ring intermediates from TNT conversion, accounting for over 40% reactions of NO₂ consumption. The abundant active intermediates are consumed mainly by the direct linking of active NO₂ and NO with the nitro groups of TNT, hydrogen-abstraction from TNT and oxidation of benzene rings. The complex interplay reactions between TNT and the active intermediates generated significantly retard the chain-like reactions for further exothermal process, decreasing the sensitivity of CL-20/TNT. The comprehensive chemical understanding on the sensitivity-decrease of CL-20/TNT thermolysis revealed by ReaxFF MD simulations can offer assistance for tuned sensitivity of new energetic CL-20-based cocrystals.