Investigating the decomposition mechanism of DNAN/DNB cocrystal explosive under high temperature using ReaxFF/lg molecular dynamics simulations

Context: DNAN/DNB cocrystals, as a newly developed type of energetic material, possess superior safety and thermal stability, making them a suitable alternative to traditional melt-cast explosives. Nonetheless, an exploration of the thermal degradation dynamics of the said cocrystal composite has heretofore remained uncharted. Consequently, we engaged the ReaxFF/lg force field modality to delve into the thermal dissociation processes of the DNAN/DNB cocrystal assembly across a spectrum of temperatures, encompassing 2500, 2750, 3000, 3250, and 3500 K. We analyzed the evolution of species, preliminary disintegration processes, and fluctuations in the quantification of terminal outcomes were examined. The findings suggest that 2,4-dinitroanisole (DNAN) undergoes a thorough phase of disassembly within a timespan of 218 ps, while 1,3-dinitrobenzene (DNB) completely decomposed within 228 ps, demonstrating that DNAN has lower thermal stability than DNB, but with no significant difference. The thermal dissociation of DNAN/DNB cocrystals at elevated temperatures reveals a triad of potential reaction sequences. Primordially, the denitration of DNAN transpires, succeeded by the denitration of DNB, culminating in the nitro-isomerization of the latter. This sequence implies that the nitro moieties within DNB possess inferior thermal resilience compared to their counterparts within the DNAN cocrystal matrix. An examination of the six resultant end products suggests a predominance of H2O, NO2, and H2 in comparison to the other byproducts, which may be indicative of the pyrolytic transformations occurring during the disassembly process.

Methods: This study first constructed the supercell model of DNAN/DNB eutectic crystal using the Materials Studio software and optimized the geometric structure of the model through the conjugate gradient algorithm. Then, the Nosé-Hoover method was used for NPT-MD simulation to further relax the model. Subsequently, molecular dynamics simulations were carried out using the LAMMPS software and the ReaxFF/lg force field. Simulation parameters were set, and NPT ensemble molecular dynamics simulations were performed at different temperatures. The simulation results were analyzed to reveal the thermal decomposition mechanism of DNAN/DNB eutectic crystal.