Abstract
Molecular dynamics (MD) simulations have been applied to investigate 1, 1-diamino-2, 2-dinitroethene (FOX-7) crystal and FOX-7 (011)-based polymer-bonded explosives (PBXs) with four typical polymers, polyethylene glycol (PEG), fluorine-polymer (F2603), ethylene-vinyl acetate copolymer (EVA) and ester urethane (ESTANE5703) under COMPASS force field. Binding energy (Ebind), cohesive energy density (CED), initiation bond length distribution, RDG analysis and isotropic mechanical properties of FOX-7 and its PBXs at different temperatures were reported for the first time, and the relationship between them and sensitivity. Using quantum chemistry, FOX-7 was optimized with the four polymers at the B3LYP/6-311++G(d,p) level, and the structure and RDG of the optimized composite system were analysed. The results indicated that the binding energy presented irregular changes with the increase in temperature. The order of binding ability of different binders to the FOX-7 (011) crystal surface is PEG > ESTANE5703 > EVA > F2603. When the temperature increases, the maximum bond length (Lmax) of the induced bond increases and the CED decreases. This result is achieved in agreement with the known experimental fact that the sensitivity of explosives increases with temperature, and they can be used as the criterion to predict the sensitivity of explosives. The descending order of Lmax is FOX-7 > F2603 > ESTANE5703≈EVA > PEG. The intermolecular interactions between FOX-7 and the four polymers were mainly weak hydrogen bonding and van der Waals interactions, and these interactions helped to reduce the bond length of C-NO2, leading to a decrease in the sensitivity of FOX-7. The addition of polymers can effectively improve the mechanical properties of explosives. Among the four polymers, EVA has the best effect on improving the mechanical properties of FOX-7 (011). At the same temperature, the modulus can be used to predict the sensitivity of high-energy materials. Cauchy pressure can predict the sensitivity of non-brittle energetic materials. The nature of the interaction between FOX-7 and the four polymers is hydrogen bonding and van der Waals force, of which hydrogen bonding is the main one. These studies are meaningful for the formulation design and sensitivity prediction of FOX-7 and its PBXs.
Highlights
The poor compatibility between high energy and low sensitivity has invariably been a major problem for researchers in the field of energetic materials. 3-nitro-1, 2, 4-triazole-5-one (NTO) [1], 5-amino-3-nitro-1H-1, 2, 4-triazole (ANTA) [2], 1, 1-diamino-2, 2-dinitroethene (FOX-7) [3] and 2, 6-diamino-3, 5-dinitor pyrazine1-oxide (LLM-105) [4] have been synthesized in order to obtain insensitive high explosives (IHE) with excellent properties
The results indicate that the error between the optimized lattice parameters and the experimental values is within 5.5%, which suggests that the COMPASS force field is suitable for simulating FOX-7 [39]
The results show that there is a certain deviation between the tensile strength of the coated FOX-7 sample and the Molecular dynamics (MD) simulation results
Summary
The poor compatibility between high energy and low sensitivity has invariably been a major problem for researchers in the field of energetic materials. 3-nitro-1, 2, 4-triazole-5-one (NTO) [1], 5-amino-3-nitro-1H-1, 2, 4-triazole (ANTA) [2], 1, 1-diamino-2, 2-dinitroethene (FOX-7) [3] and 2, 6-diamino-3, 5-dinitor pyrazine1-oxide (LLM-105) [4] have been synthesized in order to obtain insensitive high explosives (IHE) with excellent properties. 3-nitro-1, 2, 4-triazole-5-one (NTO) [1], 5-amino-3-nitro-1H-1, 2, 4-triazole (ANTA) [2], 1, 1-diamino-2, 2-dinitroethene (FOX-7) [3] and 2, 6-diamino-3, 5-dinitor pyrazine1-oxide (LLM-105) [4] have been synthesized in order to obtain insensitive high explosives (IHE) with excellent properties. Latypov et al used the BAM instrument (2 kg drop hammer) to test and found that the impact sensitivity of FOX-7 was 126 cm, while the impact sensitivity of RDX was 38 cm. They used the Julius Petri device to test and found that the friction sensitivity of FOX-7 was greater than 350 N, far lower than that of RDX (120 N) [3]. It is verified that FOX-7 has better security than RDX
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