Unraveling the Mechanism of Higher Shock Sensitivity Induced by Rapid Reactions of the Azoxy Group

Azoxy groups in explosive molecules usually act as energy enhancers but also as potential sensitivity modulators. 3,3′-Diamino-4,4’-azoxyfurazan (DAAF) is a high-nitrogen explosive characterized by the presence of an azoxy group. It exhibits relatively insensitive characteristics to mechanical stimuli such as impact and friction while also possessing characteristics of small critical diameter and sensitivity to specific shock stimuli. To gain a deeper understanding of these properties, the reactive force field parameters for DAAF were optimized, and reactive molecular dynamics (RMD) simulations were employed to study the reaction process of DAAF under shock loading. Meanwhile, the electrostatic potential (ESP) on the van der Waals surface and the bond dissociation energy of several structures were calculated by density functional theory (DFT). Then, reaction mechanisms were analyzed, and their correlations with sensitivity were explored. Results revealed that DAAF exhibits cluster evolution characteristics similar to those of TATB. However, the unique azoxy group in DAAF plays a crucial role in the initial reactions under shock loading. Key initial reactions, such as polymerization and oxygen transfer, primarily occur around the oxygen atoms in the azoxy group. After shock-induced polymerization, the dissociation energies of the chemical bonds associated with the azoxy group in DAAF molecules significantly decrease. The shock-initiated rapid reactions of the azoxy group are the important reason for DAAF’s sensitivity to shock stimuli. This suggests that the sensitivity characteristics of explosives can be modulated by introducing appropriate functional groups into the molecular structure, making them sensitive to specific stimuli.