Efficient Construction of MXene/V2O5 Nanocomposites for Optimizing the Combustion of Ammonium Perchlorate-Based Composite Solid Propellants.

The combustion performance of composite solid propellants (CSPs) significantly affects their application in the field of military and civil aircraft. Ammonium perchlorate/hydroxyl-terminated polybutadiene (AP/HTPB) composite propellants are one of the common CSPs, and their combustion performance is mainly affected by AP thermal decomposition. In this work, a simple strategy was put forward to effectively construct MXene-supported vanadium pentoxide nanocomposites (MXene/V2O5, MXV). MXene provided a good loading interface for V2O5 nanoparticles, which made MXV obtain a large specific surface area and simultaneously improved the catalytic performance of MXV for AP thermal decomposition. The catalytic experiment results showed that the decomposition temperature of AP mixed with MXV (MXV-4, 2.0 wt %) was 83.4 °C lower than that of pure AP. Moreover, the ignition delay of the AP/HTPB propellant was significantly reduced by 80.4% after adding MXV-4. The burning rate of the propellant was also increased by 202% under the catalytic action of MXV-4. Based on the above results, MXV-4 was expected to be an additive for optimizing the burning process of AP-based composite solid propellants.

Molecular dynamics simulation of CL20/DNDAP cocrystal-based PBXs.

CONTEXT: CL-20/DNDAP cocrystal is a promising new type of explosive with exceptional energy density and detonation parameters. However, compared to TATB, FOX-7 and other insensitive explosives, it still has higher sensitivity. In order to decrease the sensitivity of CL20/DNDAP cocrystal explosive, in this article, a CL20/DNDAP cocrystal model was established, and six different types of polymers, including butadiene rubber (BR), ethylene-vinyl acetate copolymer (EVA), polyethylene glycol (PEG), hydroxyl-terminated polybutadiene (HTPB), fluoropolymer (F2603), and polyvinylidene difluoride (PVDF), were added to the three cleaved surfaces of (1 0 0), (0 1 0) and (0 0 1) to obtain polymer-bonded explosives (PBXs). Predict the effects of different polymers on the stability, trigger bond length, mechanical properties, and detonation performance of PBXs. Among the six PBX models, CL-20/DNDAP/PEG model exhibited the highest binding energy and the lowest trigger bond length, indicating that CL-20/DNDAP/PEG model had the best stability, compatibility, and the least sensitivity. Furthermore, although the CL-20/DNDAP/F2603 model demonstrated superior detonation capabilities, it should be noted that this model displayed low levels of compatibility. Overall, CL-20/DNDAP/PEG model exhibited the superior comprehensive properties, thereby demonstrating that PEG is a more suitable binder option for PBXs based on the CL20/DNDAP cocrystal. METHODS: The properties of CL-20/DNDAP cocrystal-based PBXs were predicted by molecular dynamics (MD) method under Materials Studio software. The MD simulation time step was set at 1fs and the total MD simulation time was 2ns. The Isothermal-isobaric (NPT) ensemble was used for the 2ns of MD simulation. The COMPASS force field was used, and the temperature was set at 295K.

Noncovalent Interactions and Crystal Structure Prediction of Energetic Materials.

The crystal and molecular structures, intermolecular interactions, and energy of CL-20, HATO, and FOX-7 were comparatively predicted based on molecular dynamic (MD) simulations. By comparison, the 2D fingerprint plot, Hirshfeld surface, reduced density gradient isosurface, and electrostatic potential surface were studied to detect the intermolecular interactions. Meanwhile, the effects of vacuum and different solvents on the crystal habit of CL-20, HATO, and FOX-7 were studied by AE and MAE model, respectively. The energy calculation was also analysed based on the equilibrium structures of these crystal models by MD simulations. Our results would provide fundamental insights for the crystal engineering of energetic materials.

Large-Area Nanosphere Self-Assembly Monolayers for Periodic Surface Nanostructures with Ultrasensitive and Spatially Uniform SERS Sensing.

Colloidal lithography provides a rapid and low-cost approach to construct 2D periodic surface nanostructures. However, an impressive demonstration to prepare large-area colloidal template is still missing. Here, a high-efficient and flexible technique is proposed to fabricate self-assembly monolayers consisting of orderly-packed polystyrene spheres at air/water interface via ultrasonic spray. This "non-contact" technique exhibits great advantages in terms of scalability and adaptability due to its renitent interface dynamic balance. More importantly, this technique is not only competent for self-assembly of single-sized polystyrene spheres, but also for binary polystyrene spheres, completely reversing the current hard situation of preparing large-area self-assembly monolayers. As a representative application, hexagonal-packed silver-coated silicon nanorods array (Si-NRs@Ag) is developed as an ultrasensitive surface-enhanced Raman scattering (SERS) substrate with very low limit-of-detection for selective detection of explosive 2,4,6-trinitrotoluene down to femtomolar (10-14 m) range. The periodicity and orderliness of the array allow hot spots to be designed and constructed in a homogeneous fashion, resulting in an incomparable uniformity and reproducibility of Raman signals. All these excellent properties come from the Si-NRs@Ag substrate based on the ordered structure, open surface, and wide-range electric field, providing a robust, consistent, and tunable platform for molecule trapping and SERS sensing for a wide range of organic molecules.

Computational analysis the relationships of energy and mechanical properties with sensitivity for FOX-7 based PBXs via MD simulation.

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 (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 > F2603. 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 > 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.

Exploring the Coordination Effect of GO@MOF-5 as Catalyst on Thermal Decomposition of Ammonium Perchlorate.

Prepared composite materials based on [Zn4O(benzene-1,4-dicarboxylate)3] (MOF-5) and graphene oxide (GO) via a simple green solvothermal method, at which GO was used as platform to load MOF-5, and applied to the thermal decomposition of AP. The obtained composites were characterized by various techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption, Fourier transform infrared (FT-IR), differential scanning calorimetry and thermalgravimetric (DSC-TG). The analyses confirmed that the composite material (GO@) MOF-5 can not only improve the decomposition peak temperature of AP from the initial 409.7 °C to 321.9 °C, but also can improve the enthalpy (△H) from 576 J g-1 to 1011 J g-1 and reduce the activation energy (Ea), thereby accelerating the decomposition reaction. The high-specific surface area of the MOF material can provide a large number of active sites, so that the transition metal ions supported thereon can participate more effectively in the electron transfer process, and GO plays its role as a bridge by its efficient thermal and electrical conductivity. Together, accelerate the thermal decomposition process of AP.

Preparation of multi-scale FOX-7 particles and investigation of sensitivity and thermal stability.

Multi-scale ultrafine 1,1-diamino-2,2-dinitroethene (FOX-7) samples with different particle size were fabricated and specifically, nano-FOX-7 was successfully prepared by a green mechanophysical milling method. All samples were characterized by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). Impact and friction sensitivities of the samples were tested and thermal analysis was performed by differential scanning calorimetry (DSC) and thermogravimetry (TG). Ultrafine particles with a mean size of 40 nm, 0.9 µm and 3.4 µm respectively showed less sensitivity than raw FOX-7, whose particles size was about 20 µm. The critical drop height H 50 of ultrafine FOX-7 increased from 129 cm to 172 cm, 142 cm and 136 cm, respectively and the friction sensitivity reduced from 32% to 8%, 16% and 20%, respectively. Furthermore, the apparent activation energy of ultrafine particles increased compared with raw materials, which suggested the thermal stability of the ultrafine particles was improved.

Reduce the Sensitivity of CL-20 by Improving Thermal Conductivity Through Carbon Nanomaterials.

The graphene (rGO) and carbon nanotube (CNT) were adopted to enhance the thermal conductivity of CL-20-based composites as conductive fillers. The microstructure features were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD), and tested the properties by differential scanning calorimeter (DSC), static electricity accumulation, special height, thermal conductivity, and detonation velocity. The results showed that the mixture of rGO and CNT had better effect in thermal conductivity than rGO or CNT alone under the same loading (1 wt%) and it formed a three-dimensional heat-conducting network structure to improve the heat property of the system. Besides, the linear fit proved that the thermal conductivity of the CL-20-based composites were negatively correlated with the impact sensitivity, which also explained that the impact sensitivity was significantly reduced after the thermal conductivity increased and the explosive still maintained better energy.

One-Step Ball Milling Preparation of Nanoscale CL-20/Graphene Oxide for Significantly Reduced Particle Size and Sensitivity.

A one-step method which involves exfoliating graphite materials (GIMs) off into graphene materials (GEMs) in aqueous suspension of CL-20 and forming CL-20/graphene materials (CL-20/GEMs) composites by using ball milling is presented. The conversion of mixtures to composite form was monitored by scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). The impact sensitivities of CL-20/GEM composites were contrastively investigated. It turned out that the energetic nanoscale composites based on CL-20 and GEMs comprising few layers were accomplished. The loading capacity of graphene (reduced graphene oxide, rGO) is significantly less than that of graphene oxide (GO) in CL-20/GEM composites. The formation mechanism was proposed. Via this approach, energetic nanoscale composites based on CL-20 and GO comprised few layers were accomplished. The resulted CL-20/GEM composites displayed spherical structure with nanoscale, ε-form, equal thermal stabilities, and lower sensitivities.