Thermal decomposition and shock response mechanism of crystalline and amorphous 2,4-dinitroanisole (DNAN) by ReaxFF/lg reactive molecular dynamics simulations

Abstract

DNAN (2,4-dinitroanisole) is a popular melt-cast carrier explosive in the field of insensitive ammunition. The decomposition mechanisms of crystalline and amorphous DNAN were explored in this work through ReaxFF-lg molecular dynamic simulations under constant temperature (2000 K, 2500 K and 3000 K), programmed heating (10 K/ps) and the multiscale shock technique (MSST) (8 km/s, 9 km/s and 10 km/s). The evolution of initial decay reactions, number of products and clusters were performed to reveal the differences in the decomposition mechanisms between crystalline and amorphous of DNAN. Initial molecules of crystals were consumed faster in constant temperature simulations, while initial molecules of amorphous were consumed faster at MSST simulations. The O-C bond breakage was the most important thermolysis reaction and dimerization reaction was the most important shock reaction. Dimerization, intermolecular hydrogen transfer, and intermolecular oxygen transfer occur only at constant temperature and MSST simulations, and direct dissociation reactions of OH groups occur only in the amorphous case. Products analysis showed that CH3O was very important product in all simulations. Clusters analysis showed that the number of clusters in the crystals was greater than in the amorphous case for all shock velocities at MSST simulations. The fitted activation energies showed that the crystalline case was more susceptible to thermal decomposition reactions, and the fitted the initiation pressures for crystalline DNAN was 13.58 GPa, which was higher than the experimental value. There was no doubt that the molecular packing style would affect their decomposition behaviors. These results could help to increase the understanding for decomposition mechanisms of crystalline and amorphous energetic materials.