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In this paper, a primary model is established for MD (molecular dynamics) simulation for the PBXs (polymer-bonded explosives) with RDX (cyclotrimethylene trinitramine) as base explosive and PS as polymer binder. A series of results from the MD simulation are compared between two PBX models, which are represented by PBX1 and PBX2, respectively, incl...
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... 2 gives E N-N data and its components for PBX1 and PBX2, which are found unchanged. Table 3 shows the mechanical properties such as tensile modulus, shear mod- ulus, bulk modulus, and Poisson's ratio for PS1, PS2, PBX1, and PBX2. It is seen that for the two models, PBX1 and PBX2, the structure, energy and mechanical properties do not have much change. ...
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... 25 According to the principle of smallest bond order (PBSO), the smaller the bond order of the trigger bond in the chemical structure of a group of energetic compounds, the greater the sensitivity. 26,27 This principle has been applied to predict the impact sensitivity for different kinds of energetic materials. In brief, for a certain type of chemical bond, the longer the bond length, the less stable the bond is, the more likely it is to break during pyrolysis, and the more sensitive the molecule is. ...
Molecular dynamics (MD) simulations were performed on the energetic molecular perovskite (C6H14N2)[NH4(ClO4)3], with excellent detonation properties, thermal stability, and high specific impulse, which is a potential replacement for AP as the next generation propellants. The cohesive energy density, binding energy, pair correlation function, maximum bond length (Lmax) of the N–H trigger bond, and mechanical properties of the (C6H14N2)[NH4(ClO4)3] were reported. The calculated cohesive energy density and binding energy decrease with increasing temperature, indicating a gradual decrease in the thermal stability with temperature. In addition, H···O hydrogen bonding interactions have been found based on the results of pairwise correlation functions. The maximum length (Lmax) of the N–H trigger bond was calculated and used as a criterion to theoretically judge the impact sensitivity. The maximum bond length of the N–H trigger bond grows gradually with temperature; however, it does very slightly yet gradually above 373 K. This suggests that an increase in temperature leads to a higher impact sensitivity and lower thermal stability. However, this effect becomes less pronounced when the temperature surpasses 373 K. Moreover, the calculated mechanical data indicate that as the temperature rises, the material’s stiffness, hardness, yield strength, and fracture strength all decrease. The material’s ductility shows an upward trend with increasing temperature, reaching its peak at 373 K and subsequently declining as the temperature continues to rise.
... After the equilibration run, production runs of 1 ns were performed, during which data were collected with 10 fs sampling intervals for analysis. In this paper, all simulations were conducted utilizing a COMPASS (condensed-phase optimized molecular potentials for atomistic simulation studies) force field [40], which was suitable for MD simulation of the condensed phase, especially for nitramine explosives [16,[41][42][43][44]. ...
... An equilibration run was performed for 5 ns After the equilibration run, production runs of 1 ns were performed, during which data were collected with 10 fs sampling intervals for analysis. In this paper, all simulations were conducted utilizing a COMPASS (condensed-phase optimized molecular potentials for atomistic simulation studies) force field [40], which was suitable for MD simulation o the condensed phase, especially for nitramine explosives [16,[41][42][43][44]. ...
Binders mixed with explosives to form polymer-bonded explosives (PBXs) can reduce the sensitivity of the base explosive by improving interfacial interactions. The interface formed between the binder and matrix explosive also affects the thermal conductivity. Low thermal conductivity may result in localized heat concentration inside the PBXs, causing the detonation of the explosive. To investigate the binder–explosive interfacial interactions and thermal conductivity, PBXs with polyurethane as the binder and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/2,4,6-trinitrotoluene (CL-20/TNT) co-crystal as the matrix explosive were investigated through molecular dynamics (MD) simulations and reverse non-equilibrium molecular dynamics (rNEMD) simulation. The analysis of the pair correlation function revealed that there are hydrogen bonding interactions between Estane5703 and CL-20/TNT. The length of the trigger bonds was adopted as a theoretical criterion of sensitivity, and the effect of polymer binders on the sensibility of PBXs was correlated by analyzing the interfacial trigger bonds and internal trigger bonds of PBXs for the first time. The results indicated that the decrease in sensitivity of CL-20/TNT mainly comes from the CL-20/TNT contact with Estane5703. Therefore, the sensitivity of CL-20/TNT-based PBXs can be further reduced by increasing the contact area between CL-20/TNT and Estane5703. The thermal conductivity of PBXs composed of Estane5703 and CL-20/TNT (0 0 1), (0 1 0) and (1 0 0) crystal planes, respectively, were calculated through rNEMD simulations, and the results showed that only the addition of Estane5703 to the (1 0 0) crystal plane can improve the thermal conductivity of PBX100.
... In this article, the sensitivity of CL-20/ bicyclo-HMX cocrystal is judged by theoretical method. The interaction energy of trigger bond [41][42][43][44] (also called trigger bond energy) theory is chosen to predict the sensitivity of CL-20/bicyclo-HMX cocrystal explosive and judge its safety. Trigger bond is generally defined as the chemical bond that has the lowest value of bond strength. ...
In this article, a novel energetic cocrystal composed of CL-20 and bicyclo-HMX was designed. The crystal models of pure components (CL-20, and bicyclo-HMX) and CL-20/bicyclo-HMX energetic cocrystal models with different molecular ratios were established. Molecular dynamic (MD) method was adopted to optimize the cocrystal structure and predict its properties, including sensitivity, stability, mechanical properties, and energetic performance. Results show that the trigger bond (N-NO2 bond) energy in CL-20/bicyclo-HMX energetic cocrystal model is increased, meaning that the trigger bond strength is enhanced and the cocrystal explosive should have lower mechanical sensitivity than pure CL-20. The CL-20/bicyclo-HMX cocrystal model with molecular ratio of 2:1 has higher value of binding energy, implying that the intermolecular interaction is stronger and this energetic cocrystal model is more stable. The engineering moduli (bulk modulus, shear modulus, and tensile modulus) of CL-20/bicyclo-HMX energetic cocrystal models are decreased, while Cauchy pressure is increased, indicating that the energetic cocrystal has better mechanical properties than CL-20. The energy density of CL-20/bicyclo-HMX cocrystal explosive is lower than pure CL-20, but much higher than bicyclo-HMX, the energetic cocrystal with molecular ratio of 10:1 ~ 2:1 can be regarded as potential candidate for high energy density compound (HEDC).
... theoretical prediction methods. In this article, based on the classical theory of sensitivity, i.e., the "hot spot" hypothesis [31] and the "trigger bond" hypothesis [32], the interaction energy of trigger bond (also called trigger bond dissociation energy) [33][34][35][36] is selected as a rule to judge the sensitivity of primitive and defective CL-20/ HMX cocrystal models. ...
Crystal defect in energetic materials will directly affect its crystal structure and physicochemical properties, including mechanical sensitivity, thermal stability, mechanical properties, energetic performance, etc. In this article, the primitive and defective CL-20/HMX cocrystal models were established and the influence of crystal defects (including adulteration defect, dislocation defect and vacancy defect) on properties of CL-20/HMX cocrystal explosive was investigated by MD method. Results show that the trigger bond strength (N–N chemical bond) of CL-20 molecules in defective CL-20/HMX cocrystal models is lower than primitive cocrystal model and the mechanical sensitivity is increased. Compared with primitive cocrystal model, the binding energy between CL-20 and HMX molecules in defective models is decreased, meaning that the stability of defective models is weakened. The primitive cocrystal model has higher value of shear modulus, tensile modulus, and bulk modulus and lower value of Cauchy pressure than defective models, indicating that the rigidity and rupture strength of defective models are lowered. The density and detonation performance of defective CL-20/HMX cocrystal models are lower than primitive model, implying that the energy density is declined. Therefore, crystal defect can bring a negative influence on mechanical sensitivity, stability and energetic performance of CL-20/HMX cocrystal explosive, and the effect of vacancy crystal defect is more obvious and severe.
... To predict the sensitivity and estimate safety of EMs, tremendous efforts have been paid to seek for the factors that may determine mechanical sensitivity. In this work, based on the hot spot theory [34] and trigger bond theory [35], we adopted the trigger bond length, interaction energy of trigger bond, and cohesive energy density [36][37][38][39] as a basic criterion to judge the sensitivity of raw CL-20, LLM-105, and CL-20/LLM-105 cocrystal explosive. Besides, the sensitivity of cocrystal explosive was compared with that of pure CL-20 to estimate the desensitizing effect of cocrystallization method. ...
The hexanitrohexaazaisowurtzitane/2,6-diamino-3,5-dinitropyrazine-1-oxide (CL-20/LLM-105) cocrystal models with different component ratios were established by the substitution method. The stability, sensitivity, energetic performance, and mechanical properties of CL-20, LLM-105, and CL-20/LLM-105 cocrystal models were predicted by the molecular dynamics method. The results show that the CL-20/LLM-105 cocrystal model with component ratio of 2:1 has the highest value of binding energy and is the most stable model. The cocrystal model has shorter trigger bond length than pure CL-20, but higher value of trigger bond energy and cohesive energy density, which implies that the sensitivity of cocrystal explosive is decreased. The cocrystal explosive has lower energy density than CL-20, but the cocrystal explosive with molar ratio of 10:1~2:1 still has high energy density and can be regarded as novel high energy density compound (HEDC). The tensile modulus, shear modulus, and bulk modulus of cocrystal models are decreased, Cauchy pressure is increased, meaning that the mechanical properties is improved. In a word, the CL-20/LLM-105 cocrystal explosive with component ratio of 2:1 has the best stability, lowest mechanical sensitivity, most desirable mechanical properties, and high energy density, it is very promising to become a novel HEDC.
... Through the above comparisons, we find that the non-covalent interactions between TNT and CL-20 are mainly vdW forces and hydrogen bonding, while those between HMX and CL-20 are mainly vdW forces. Based on the principle of the smallest bond order (PSBO) calculated via quantum chemistry, more sensitive energetic compounds usually contain a smaller bond order of trigger bond in molecules, and it is known that the CL-20 component in TNT/CL-20 decomposes earlier in detonation because CL-20 is more sensitive [24,53]. Therefore, the stability of the N-NO2 bond in CL-20 as a trigger bond was investigated using the Mayer BOD approach (Table 2) [44,54]. ...
Inspired by the recent cocrystallization and theory of energetic materials, we theoretically investigated the intermolecular vibrational energy transfer process and the non-covalent intermo-lecular interactions between explosive compounds. The intermolecular interactions between 2,4,6-trinitrotoluene (TNT) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and between 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) and CL-20 were studied using calculated two-dimensional infrared (2D IR) spectra and the independent gradient model based on the Hirshfeld partition (IGMH) method, respectively. Based on the comparison of the theoretical infrared spectra and optimized geometries with experimental results, the theoretical models can effectively reproduce the experimental geometries. By analyzing cross-peaks in the 2D IR spectra of TNT/CL-20, the intermolecular vibrational energy transfer process between TNT and CL-20 was calculated, and the conclusion was made that the vibrational energy transfer process between CL-20 and TNTII (TNTIII) is relatively slower than between CL-20 and TNTI. As the vibration energy transfer is the bridge of the intermolecular interactions, the weak intermolecular interactions were visualized using the IGMH method, and the results demonstrate that the intermolecular non-covalent interactions of TNT/CL-20 include van der Waals (vdW) interactions and hydrogen bonds, while the in-termolecular non-covalent interactions of HMX/CL-20 are mainly comprised of vdW interactions. Further, we determined that the intermolecular interaction can stabilize the trigger bond in TNT/CL-20 and HMX/CL-20 based on Mayer bond order density, and stronger intermolecular interactions generally indicate lower impact sensitivity of energetic materials. We believe that the results obtained in this work are important for a better understanding of the cocrystal mechanism and its application in the field of energetic materials.
... Cohesive energy density (CED) refers to the energy required for 1mol condensate in unit volume to overcome the intensification of intermolecular interaction, with the unit of kJ/cm 3 and the calculation formula of [16] ...
In order to explore the influence of doping defects on the properties of CL-20 / HMX eutectic explosive, the models with different doping rates were calculated by molecular dynamics method. The results show that compared with the non-doped crystal model, the binding energy in the doped model is reduced by 0.332%~11.805%; The initiation bond length increased by 0.9%~4.6%; The binding diatomic interaction energy is reduced by 2.31%~15.46%; The cohesive energy density decreased by 19.75%~50.39%; The decreasing range of density is 0.697%~4.450%; The reduction range of detonation velocity is 0.744%~5.449%; The reduction range of explosion pressure is 1.864%~12.841%; The bulk modulus decreased by 0.4844~6.7461GPa, the shear modulus decreased by 0.9442~5.2329GPa, and the tensile modulus decreased by 2.0431~12.5374GPa. It shows that doping defects will reduce the stability, safety and detonation performance of explosives, and make the hardness, fracture resistance and rigid strength of explosives worse.
... For energetic compounds, there exists a criterion to theoretically judge the relative sensitivity [22]. According to Principle of Smallest Bond Order (PBSO) based on quantum chemical calculation, for a series of energetic compounds with smaller bond order of trigger bond in molecular means the compound is more sensitive [36,37]. This principle has been used extensively in the prediction of impact sensitivity for various types of energetic compounds. ...
In order to better understand the role of binder content, molecular dynamics (MD) simulations were performed to study the interfacial interactions, sensitivity and mechanical properties of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/2,4,6-trinitrotoluene (CL-20/TNT) based polymer-bonded explosives (PBXs) with fluorine rubber F2311. The binding energy between CL-20/TNT co-crystal (1 0 0) surface and F2311, pair correlation function, the maximum bond length of the N–NO2 trigger bond, and the mechanical properties of the PBXs were reported. From the calculated binding energy, it was found that binding energy increases with increasing F2311 content. Additionally, according to the results of pair correlation function, it turns out that H–O hydrogen bonds and H–F hydrogen bonds exist between F2311 molecules and the molecules in CL-20/TNT. The length of trigger bond in CL-20/TNT were adopted as theoretical criterion of sensitivity. The maximum bond length of the N–NO2 trigger bond decreased very significantly when the F2311 content increased from 0 to 9.2%. This indicated increasing F2311 content can reduce sensitivity and improve thermal stability. However, the maximum bond length of the N–NO2 trigger bond remained essentially unchanged when the F2311 content was further increased. Additionally, the calculated mechanical data indicated that with the increase in F2311 content, the rigidity of CL-20/TNT based PBXs was decrease, the toughness was improved.
... So, to some certain extent, CED can be considered as a theoretical criterion for relative thermal sensitivity. It is pointed out in the literature that the N-NO2 bond is the pyrolysis or initiation bond of nitroamine explosives [24], and the molecules with the largest bond length are the activated molecules, which are most likely to cause decomposition and initiation. The activation bonds ratio is defined as the ratio of the activated bond lengths to the total bond length distribution. ...
... So, to some certain extent, CED can be considered as a theoretical criterion for relative thermal sensitivity. It is pointed out in the literature that the N-NO 2 bond is the pyrolysis or initiation bond of nitroamine explosives [24], and the molecules with the largest bond length are the activated molecules, which are most likely to cause decomposition and initiation. The activation bonds ratio is defined as the ratio of the activated bond lengths to the total bond length distribution. ...
The internal defect is an important factor that could influence the energy and safety properties of energetic materials. RDX samples of two qualities were characterized and simulated to reveal the influence of different defects on sensitivity. The internal defects were characterized with optical microscopy, Raman spectroscopy and microfocus X-ray computed tomography technology. The results show that high-density RDX has fewer defects and a more uniform distribution. Based on the characterization results, defect models with different defect rates and distribution were established. The simulation results show that the models with fewer internal defects lead to shorter N-NO2 maximum bond lengths and greater cohesive energy density (CED). The maximum bond length and CED can be used as the criterion for the relative sensitivity of RDX, and therefore defect models doped with different solvents are established. The results show that the models doped with propylene carbonate and acetone lead to higher sensitivity. This may help to select the solvent to prepare low-sensitivity RDX. The results reported in this paper are aiming at the development of a more convenient and low-cost method for studying the influence of internal defects on the sensitivity of energetic materials.
... Sensitivity is a crucial indicator for evaluating the safety of high-energy materials. Under the stimulation of external environment such as impact, heat, friction, shock wave, etc. the difficulty of the explosion of energetic materials directly affects its synthesis, preparation, transportation, storage and use [24]. Therefore, the research on sensitivity is fundamental and significant. ...
... In much of the research in the past, individuals have used this method to do a multitude of study on hexanitrohexaazaisowurtzitane (CL-20), RDX, cyclotetramethylenetetramine (HMX), and PBX based on them and calculated the equilibrium structure, binding energy and mechanical properties of different composite systems [27][28][29][30][31][32]. To explore the microscopic theoretical criteria of the sensitivity of high-energy composite materials, the relations of sensitivity with the cohesive energy density, the bond length distribution and the mechanical properties for the system at different temperatures were also discussed [24,[33][34][35][36][37]. At present, there are few studies on the simulation of FOX-7 and its PBXs, while few reports on the research on the relations of sensitivity with structure, energy and mechanical properties for FOX-7 and its PBXs [7]. ...
... This complex change is understandable because of the many factors that affect the binding energy, and only characterizes the overall thermal stability of the system. Since the sensitivity acts within the 'hot spot' theory as a local property, E bind cannot be used to predict sensitivity [24]. ...
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 (F 2603 ), ethylene-vinyl acetate copolymer (EVA) and ester urethane (ESTANE5703) under COMPASS force field. Binding energy ( E bind ), 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 > F 2603 . When the temperature increases, the maximum bond length ( L max ) 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 L max is FOX-7 > F 2603 > 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-NO 2 , 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.
