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This article presents an experimental investigation on the fretting wear behavior of piezoceramics P51, PSnN5, and PLiS51 against an Si3N4 ceramic ball under air condition. A sphere-on-flat contact...

A novel energetic polymer binder was developed through ring opening copolymerization of 3-nitratomethyl-3-methyloxetane (NIMMO) with (HTPE) as a macroinitiator to form tri-block copolymer polyNIMMO-HTPE-polyNIMMO. The structure of tri-block copolymer was confirmed by FTIR, 1H NMR, 13C NMR and GPC. In comparison with HTPE, polyNIMMO-HTPE-polyNIMMO has a higher viscosity because of its increased molecular weight with additional ONO2 as side groups and strengthened intermolecular interaction. The glass transition temperature studies show two glass transition processes in their DSC curves. One signal around −69 °C arises from the HTPE segment, while the other signal around −30 °C is related to the terminal polyNIMMO segments in the tri-block polymers. The TGA-DTG and DSC curves indicate that polyNIMMO-HTPE-polyNIMMO has a good thermal stability and its exothermic decomposition peak is found to be around 220 °C. The kinetic parameters and the thermodynamic parameters for the thermal decomposition of polyNIMMO-HTPE-polyNIMMO-IV are obtained from the DSC data by non-isothermal methods proposed by ASTM E698 and FWO. These results demonstrate that tri-block copolymer polyNIMMO-HTPE-polyNIMO might be a potential energetic propellant binder.

Rubbers are widely used in various fields as the important sealing materials, such as window seal, door seal, valve, pump seal, etc. The fretting wear behavior of rubbers has an important effect on their sealing performance. This paper presents an experimental study on the fretting wear behavior of rubbers against the steel ball under air conditions (room temperature at 20 ± 2 °C and humidity at 40%). Three kinds of rubbers, including EPDM (ethylene propylene diene monomer), FPM (fluororubber), and NBR (nitrile–butadiene rubber), are considered in experiments. The sphere-on-flat contact pattern is used as the contact model. The influences of the displacement amplitude, normal force, frequency, and rubber hardness on the fretting wear behavior are discussed in detail. White light profiler and scanning electron microscope (SEM) are used to analyze the wear mechanism of the rubber surface. The fretting wear performances of three rubbers are compared by considering the effect of the displacement amplitude, normal force, frequency, and rubber hardness. The results show that NBR has the most stable friction coefficient and the best wear resistance among the three rubbers.

This paper discusses an in-depth experimental study on the fretting wear behavior of PVDF (polyvinylidene fluoride) piezoelectric thin film against a Si3N4 ceramic sphere under air conditions. A fretting wear device with a ball-on-plate contact configuration was applied. The changes of displacement amplitude, normal force, and applied voltage were taken into account. The friction logs were used to determine the contact state of the PVDF thin film during the fretting test. The 3D topography instrument and scanning electron microscope (SEM) were used to measure the details of the surface morphology and wear volume. The test results of PVDF thin films under different normal force, displacement amplitude, and applied voltage are summarized through the collection and analysis of experimental data. It is shown that the creep and plastic deformation lead to obvious winkles at the contact surface, which may decrease the specific wear rate of PVDF thin films.

2,4,6-Trinitrotoluene (TNT) is a class C carcinogen as rated by the Environmental Protection Agency. One of the toxicity mechanisms of TNT is the covalent binding of its metabolites to critical proteins. However, knowledge about their molecular reaction mechanisms is scarce. Herein, we have provided density functional theory (DFT) simulation evidences for the reaction mechanisms of the nitroso metabolite of TNT with the sulfhydryl group of model thiols for the first time. The results show that the solvent-mediated proton-transfer mechanism plays a significant role in the entire process. For the formation of semimercaptal, the mechanism is slightly different from the previous one where the thiolate anion attacks the nitroso group. The rearrangement of semimercaptal needs to be triggered by an acid or hydrated ion (H(3)O(+)), which is consistent with the previous assumption. The other pathway, the conversion of semimercaptal to hydroxylamine, has to overcome a higher barrier, although it does not need the participation of an acid or a hydrated ion. In addition, the details on transition states, intermediates and free energy surfaces for three reactions are given, which make up for the lack of experimental knowledge. These conclusions can help to deeply understand the toxic effects of TNT and other nitroaromatic explosives.

Molecular dynamic (MD) simulations were employed to investigate the hexanitrohexaazaisowurtzitane (CL-20) crystal, seven designed energetic poly-(phthalazinone ether sulfone ketones) (PPESKs) and PPESKs/e-CL-20 polymer–bonded explosives (PBXs). Cohesive energy density (CED) and solubility parameters (δ) were predicted for PBXs, the results indicated that stability of PBXs are related to their cohesive energy density (CED). Mechanical properties of seven polymer-bonded explosives (PPESKs/e-CL-20) were found improved in comparison with that of e-CL-20 by adding polymer binders. Young’s modulus (E), Shear modulus (G), and Bulk modulus (K) declined compare with e-CL-20. K/G ratio and Cauchy pressure C12-C44 of PBXs indicate that they have certain ductility. Radial distribution function (RDF) was utilized for analyzing the interactions between PPESKs and e-CL-20, and results demonstrate that hydrogen bond and van der Waals interactions exist between polymers and e-CL-20. The calculated oxygen balance of polymer-bonded explosives (PBXs) is lower than that of pure e-CL-20 by nearly about − 24%. Detonation properties of the polymer-bonded explosives (PBXs) were predicted based on e-CL-20 values. Detonation velocity (D) for these PBXs was predicted almost at about 8300 m s−1, and the detonation pressure (P) for these PBXs was all predicted nearly at 38 GPa.

Five novel poly-(phthalazinone ether sulfone ketone (PPESK) polymers were designed by introducing the sbndNO2, sbndNH2, sbndN3, sbndONO2 and sbndNF2 function groups into the polymer chain. The glass transition temperature (Tg), density, cohesive energy density (CED), solubility parameters (δ) and mechanical properties were simulated via the molecular dynamics (MD) method for these novel polymers. The Tg values of all these polymers were predicted above 500 K, and especially that of the sbndNH2 substituted polymer close to 600 K. Cohesive energy density (CED) and solubility parameter (δ) values of these five polymers were predicted very close at 298 K, implying that they have similar solubility. The predicted Young's modulus (E), Bulk modulus (K), Shear modulus (G) and Poisson’s ratio (γ) indicate that these polymers have good mechanical properties and plastic properties, and the K/G and Cauchy pressure (C12-C44) indicate that they have good ductility.

In the 21st century, it is bound to become an important trend for the assembly of novel micro/nano functional materials with long lifespan in the real world by using facile techniques. In this report, the concept of using a low-cost and convenient method of electrophoretic assembly and further surface functionalization by perfluoroalkyltriethoxysilane (FAS-17) modification to obtain superhydrophobic nanoscale composite coatings (e.g. Al/Bi2O3) and its first demonstration are reported. The resulting low-energy coatings with nanoparticles distributed homogeneously in nanoscale and abundant rough reticular structures possess almost perfect superhydrophobic properties with a water contact angle (WCA) of ca.170° and a negligible roll-off angle. The water droplet impact dynamics is analyzed by a high-speed photography in detail. Additionally, the superhydrophobicity and exquisite heat release performance of the products keep almost unchanged after ultra-long exposure time and high relative humidity (>90%), respectively, indicating the excellent stability and great resistance to changeable environment and wide application potential in fields of surface chemistry, materials science and engineering, physics, etc. This study provides an effective general strategy for the design and development of superhydrophobic functional composites with wide application for different experimental and industrial purposes.

2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is the most powerful commercially available explosive. This paper discusses the molecular structures and intermolecular interactions of pure e-CL-20 and three CL-20-based energetic–energetic cocrystals, CL-20/2,4-dinitro-2,4-diazapentane (DNDAP), CL-20/2,5-dinitrotoluene (DNT) and CL-20/1-methyl-3,5-dinitro-1,2,4-triazole (MDNT). The underlying mechanisms of their dramatic and divergent sensitivity and detonation performance were revealed as well. We find that CL-20/DNDAP and CL-20/DNT cocrystals arrange in layered motifs, while CL-20/MDNT features irregular but compact packing. Overall, the non-covalent interactions govern the structures of the cocrystals. Regarding sensitivity, in the case of CL-20/DNDAP and CL-20/DNT, the high impact sensitivity of CL-20 is reduced, making the two cocrystals viable explosives. Conversely, CL-20/MDNT uniquely exhibits higher impact sensitivity compared with pure CL-20, which may be caused by weak intermolecular interactions and molecular transformation of CL-20 from stable e-form to α-form. Furthermore, CL-20/MDNT possesses the greatest detonation performance due to its excellent density and high heat of formation, followed by CL-20/DNDAP and CL-20/DNT. These results confirm that a layered packing pattern and weak hydrogen bonding are among the key factors for insensitive cocrystal explosives. Meanwhile, cocrystals of CL-20 with multi-nitrogen energetic compounds have the potential to be promising high-performance energetic materials.

Molecular dynamics simulation was performed on 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), 2,4-dinitro-2,4-diazapentane (DNDAP), and CL-20/DNDAP cocrystal and composite under COMPASS force field at different temperatures. The binding energy (Ebind), radial distribution function (RDF), trigger bond length, cohesive energy density (CED) and mechanical properties were studied and compared. The results show that the binding energy of the cocrystal is evidently higher than that of the composite at the same temperature. RDF analysis reveals that hydrogen bonds and vdW forces between CL-20 and DNDAP exist in both CL-20/DNDAP cocrystal and composite, and the interactions in the cocrystal are stronger than those in the composite. The maximum trigger bond length decreases in the order e-CL-20 > CL-20/DNDAP composite > CL-20/DNDAP cocrystal. Moreover, the rigidity and stiffness of the cocrystal and composite decrease compared to that of CL-20, while the ductility and elasticity are better than that of the two pure components. These results demonstrate that CL-20/DNDAP cocrystal might be very promising in explosive applications.

Molecular dynamics (MD) simulations were carried out to study the glass transition temperature and mechanical properties of glycidyl azide polymer (GAP) most widely used in propellants and explosives as an energetic binder. Other three polymers derived from GAP with different side groups were designed and simulated under the COMPASS force field, with the ensembles of constant particle number, volume, temperature (NVT) and constant particle number, pressure, temperature (NPT). It was found that the densities and free volumes of polymers changed regularly along with the decrease of temperature and the transition occurred at the turning point. Thus the glass transition temperatures (Tg) were predicted in two methods based on density and free volume theory. The simulation results showed that the introduction of –NO2 made important contribution on reducing the Tg of polymers, and the probable mechanism was discussed. Moreover, several mechanical properties of four pure polymer systems such as Young’s modulus, Shear modulus, Bulk modulus and Poisson’s ratio, etc, were calculated. The calculated results revealed that the single introduction of –NO2 increased the mechanical properties parameters more obviously than other two polymers. Overall, a new method was used for GAP modification in order to improve its mechanical properties at low temperatures, and provides some guidance to the GAP modification via changing substituent groups of side chain.

A novel porous Al/CuO nanothermite was successfully synthetized by utilizing the controllable electrophoretic deposition (EPD) method. The morphology and phase composition of the CuO and Al/CuO films were investigated in detail by field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). When the pH of the solution was 2.0, the surface area of the Al/CuO film was able to reach 495.6 m 2 /g, which was much higher than that of films grown at pH 1.0, 3.0 or 4.0. Meanwhile, the combustion performance and energy outputs were coincident with the results mentioned above. At pH 2.0, bright flames were observed after ignition, and the released heat of the nanothermite reaction reached 3.49 kJ/g, exhibiting excellent combustion performance and enhanced energy output.

The properties of borosiloxane-containing copolyimides with borosiloxane in the main chain and in the side chain were studied. Two series of borosiloxane-containing copolyimides were synthesized by the reaction of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) and 2,3′,3,4′-biphenyltetracarboxylic dianhydride (a-BPDA) with p-phenylenediamine (PDA), 4,4′-oxydialinine (4,4′-ODA) and different borosiloxane diamine monomers (BSiAs). The synthesized borosiloxane-containing copolyimides exhibited better solubility than borosiloxane-free copolyimides and showed high glass transition temperatures (320–360 °C), excellent thermal stability (570–620 °C for T10), great elongation at break (10% − 14%) and a low coefficient of thermal expansion (14–24 ppm °C−1). More specifically, the copolyimides containing BSiA-2 formed nano-scale protrusions and the copolyimides containing BSiA-1 formed micro-scale protrusions. The contact angles of the copolyimides increased from 72° for neat copolyimide to 96° for 5% of borosiloxane in the main chain of the copolymer up to 107° for 10% of borosiloxane in the side chain of the copolymer. © 2017 Society of Chemical Industry

Al/CuO nanoenergetic materials with nanotube and nanorod morphologies were prepared and investigated in this study. The CuO nanotubes and nanorods synthesized by chemical etching are homogenous on a large scale, with an external diameter in the range of 100– 200 nm and typical lengths of 5– 7 μm. Each of these CuO nano-arrays was deposited on nano-Al by electrophoretic deposition. Using the Brunauer-Emmett-Teller method, the Al/CuO nanotube composite is determined to have a larger specific surface area (43.20 m2/g) than that of the Al/CuO nanorod composite (16.75 m2/g). The energy released from the Al/CuO nanotubes is approximately to 3264 J/g, which is higher than that released from the Al/CuO nanorods (2013 J/g). The combustion flames for the Al/CuO nanotubes are also more rapid and violent. It is speculated that the excellent output of energy and outstanding combustion performance of the Al/CuO nanotubes could be ascribed to their tubular architecture, which has a larger specific surface area enhances the intimate contact and mass transmission between fuel and oxide. Keywords: Nanoenergetic materials, Intimate contact, Specific surface area, Thin films

In present study, a novel and facile strategy of electrophoretic deposition (EPD) with following perfluorodecyltriethoxysilane (FAS-17) modification is successfully introduced to fabricate superhydrophobic ternary composites-Al x Ni y (Bi 2 O 3 ) z with excellent superhydrophobic and thermal stability property. The chemical composition, morphology and heat-release performance of the products were analyzed by XRD, FESEM, FT-IR, EDX, DSC and a high-speed camera, respectively. The stable suspension consisted of isopropyl alcohol and additive-polyethyleneimine. The deposition mechanism of ternary composite coating was firstly given, and EPD kinetics were investigated in detail. Moreover, the water contact angle and roll-off angle of superhydrophobic Al x Ni y (Bi 2 O 3 ) z with as well as significant water bouncing properties can reach to 169 ± 2° and ca. 1°, respectively. In addition, superhydrophobicity and internal chemical energy (ca. 2 MJ kg −1 ) of products all keep almost stable after 300 days, exhibiting a high value of practical application. Thus, this study provides a promising and low cost method for the synthesis of various superhydrophobic composites with long-term storage stability in different humidity environments and zones, even underwater.

A bicyclooxacalixarene cage with triangular prism structure was synthesized by a one-pot SNAr reaction. The structure of the oxacalixarene cage 1 was characterized by NMR, MS spectra, and X-ray crystal structure analyses. In the solid state, the molecular cage was assembled into an interlaced porous network structure. Gas adsorption studies indicated that cage 1 exhibited high CO2/N2 selectivity of 106.

The kinetics and the products of thermal decomposition of 2,4,6-triazidopyrimidine in the melt were investigated by thermogravimetry, manometry, mass-spectrometry, and IR spectroscopy. The kinetic and activation parameters of the processes were found. Nitrogen was the only gaseous product of the reaction. The structure of the solid reaction product was determined. A mechanism of thermal decomposition of 2,4,6-triazidopyrimidine, including elimination of a nitrogen molecule to give nitrene in the initial step, was proposed. The unusually high pre-exponential factor in the Arrhenius equation (1016.7±0.7 s–1) was attributed to a significant contribution of polymerization (polycondensation) to the overall process, resulting in the formation of carbon—nitrogen two-dimensional networks.

The high energy density compound octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and the strong exothermic compound LiH represent an excellent principal explosive and an active fuel, respectively. Herein, the energetic characteristics of HMX-based explosives are explored by adding LiH as fuel additive. The detonation parameters of HMX-based explosives containing LiH were tested with free-field explosion experiments and compared with those of traditional TNT, HMX, and aluminized explosives. The results show that the explosives exhibit higher energy and present preferable explosion effect when LiH is added as an explosive ingredient. The improvement of impulse is more than 32.8 % at 2 m. The shock wave peak overpressure increases by almost 40 % at a distance of 3 m from detonation center specially for the explosive containing both LiH and Al additives. Elemental H and Li are expected to release tremendous energy to effectively improve the explosives instant damage power, but the detonation duration is shorter than that of Al-containing mixed explosives, which may limit the advantage over Al in the impulse. Li2CO3 powder is the solid product of HMX/LiH, which explains the LiH oxidation during the explosion. The exothermic processes in the formation are the reason for the increased energy of HMX/LiH explosives. These results can provide guidance to a potential energetic system formed by HMX and LiH.

A series of copolyimides were prepared by thermal imidization of poly(amic acid)s (PAAs) derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA), 2,3′,3,4′-biphenyltetracarboxylic dianhydride (a-BPDA), p-phenylenediamine (PDA) and 4,4′-oxydialinine (4,4′-ODA) commonly used for the production of commercial polyimides. The flexible copolyimide films were obtained from that the molar ratio of s-BPDA, a-BPDA, PDA and 4,4′-ODA was 9:1:8:2 (Co-PIs-3), 8:2:9:1 (Co-PIs-5) and 8:2:8:2 (Co-PIs-6). These obtained copolyimide films were characterized by Fourier transform-infrared spectroscopy(FT-IR), wide angle X-ray (WAXD), Thermogravimetric (TG), dynamic mechanical thermal analysis (DMA), thermomechanical analysis (TMA), field-emission scanning electron microscopy (FE-SEM) and mechanical properties measurement. The results showed that three copolyimides remained semi-crystalline and exhibited high glass transition temperature (Tg), high thermal stability, great ultimate tensile strength and low coefficient of thermal expansion (CTE). The Co-PIs-5 had lower crystallinity, lower CTE, greater elongation at break, higher Tg and thermal stability and the greater dense extent, compared with Co-PIs-3 and Co-PIs-6. Structure and property relations of the prepared polyimides were also briefly discussed. The results revealed that the copolymerization of s-BPDA/PDA with a small number of 4,4′-ODA/a-BPDA was a useful means for enhancing flexibility without sacrificing low CTE.

3,6-Dinitropyrazolo[4,3-c]pyrazole (DNPP, 4) was prepared using an efficient modification process. Various neutral energetic derivatives of DNPP were synthesized from N-functionalization of imide (NH) group. All compounds were fully characterized by 1H and 13C nuclear magnetic resonance spectroscopy, infrared spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). The crystal structures of compounds 4·2H2O, 12 and 15 were confirmed by single-crystal X-ray diffraction, showing extensive hydrogen-bonding. The densities of neutral derivatives ranged from 1.74 to 1.95 g cm−3, and all compounds have positive heats of formation in the range of 18.8 to 863 kJ mol−1. Based on the measured densities and calculated heats of formation, theoretical performance calculations, including detonation pressures (27.1–41.5 GPa) and velocities (7819–9364 m s−1), were carried out using the Gaussian 09 program and Kamlet–Jacobs equations, and they compare favorably with those of TNT and RDX. These properties make them potential and competitive for use as new high energy-density materials.

The β → γ polymorphic transformation (PT) in polycrystalline 1,1-diamino-2,2-dinitroethylene (DADNE) was studied by isothermal calorimetry. The kinetics of the β → γ PT, like that of the α → β process studied earlier, follows the first-order autocatalytic equation. The rate constants and activation energy of the process were determined. The kinetics of the reverse β → α and γ → α PTs in DADNE was studied by IR spectroscopy. The rates of the β → α and γ → α PTs follow first-order kinetics with the rate constants that depend on morphological features of the crystals. The general features of the kinetics of direct and reverse polymorphic transformations in molecular crystals of energetic compounds are discussed.

A series of copolyimides were prepared by thermal imidization of polyamide acids derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 2,3′,3,4′-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, p-phenylenediamine and 4,4′-oxydialinine commonly used for the production of commercial polyimides. The flexible copolyimide films characterized by ultra-low coefficient of thermal expansion were obtained and characterized by FTIR, WAXD, TG, DMA, TMA, FE-SEM and tensile properties measurement. The results showed that three copolyimides remained semi-crystalline and exhibited high glass transition temperature, high thermal stability, and great ultimate strength.

The detailed degradation mechanism of an insensitive explosive, 2,4-dinitroanisole (DNAN), in advanced oxidation processes (AOPs) was investigated computationally at the M06-2X/6-311 + G(d,p)/SMD level of theory. Results obtained show that the addition-elimination reaction is the dominant mechanism. The phenol products formed can continue to be oxidized to benzoquinone radicals that are often detected by experiments and may be the initial reactants of ring-opening reactions. The H-abstraction reaction is an unavoidable competing mechanism; the intermediate generated can also undergo the process of addition-elimination reaction. The nitro departure reaction involves not only hydroxyl radical (•OH), but also other active substances (such as •H). More importantly, we found that AOP technology can easily degrade DNAN, similar to TNT and DNT. Thus, this method is worth trying in experiments. The conclusions of this work provide theoretical support for such experimental research. Graphical abstract Possible pathways of degradation by •OH radicals in advanced oxidation processes (AOPs) of the typical insensitive explosive 2,4-dinitroanisole (DNAN) were investigated by density functional theory (DFT) methods. Based on the Gibbs free energy barriers and intermediates, the dominant reaction mechanism was determined. The conclusions will be helpful in utilizing AOP technology to remove DNAN pollution.

In order to cure hydroxyl-terminated polybutadiene (HTPB) at room temperature, Trimethylisophthtalodinitrile oxide (TINO) was synthesized in four steps from mesitylene with total yield of 42.0%. Its structure was characterized by FT-IR 1H NMR and 13C NMR. Make curing agent TINO/HTPB equals 12, 14, 16, 18 and 20% to prepare the dumbbell-shaped cross-linked polymers. The FT-IR, tensile strength, DSC, TG and contact angle of the cross-linked polymers were tested and analyzed. With the increasing of TINO, tensile strength of cross-linked polymers increased from 0.077 to 0.300 MPa and the elongation at break decreased from about 437 to 104%. The Tg of the crosslink polymers are −75.01, −73.92, −73.42, −70.09 and −71.78 °C, respectively. The contact angles are 116.91°, 100.66°, 93.68°, 86.25° and 87.35°. The results showed that TINO can cure HTPB under room temperature and the cross-linked polymers are expected to be used in the composite solid propellant.

The synthesis of three heat-resistant explosive materials: 4,8-di(2,4,6-trinitrophenyl)difurazano[3,4-b:3′,4′-e]pyrazine (1), 4,8-di(2,4-dinitrophenyl)difurazano[3,4-b:3′,4′-e]pyrazine (2), 4-amino-8-(2,4,6-trinitrophenyl)difurazano[3,4-b:3′,4′-e]pyrazine (3),were reported and characterized by 1H NMR,13C NMR, IR as well as elemental analysis. X-ray crystallographic analysis confirmed the structure of 2, as well as displaying intermolecular hydrogen bonding. The thermal behaviors of these compounds were studied with differential scanning calorimetry (DSC) and thermal gravity-differential thermal gravity analysis (TG-DTG) methods. All the compounds showed good thermal stability with exothermic decomposition peaks in the range of 283 °C to 415 °C, on DSC. The sensitivities and calculated explosive performances were also reported for these energetic materials. All the results showed that polynitroaromatic substituted difurazano[3,4-b:3′,4′-e]pyrazines have the potential to be useful heat-resistant explosive materials.

Molecular dynamics simulations have been employed to study the e-CL-20-based PBXs under COMPASS force field. e-CL-20 was chosen as the base explosive due to its higher energy, density and detonation performance than conventional explosives. Four polymers, GAP, GAP-NH2, GAP-NO2 and GAP-NH2-NO2 were added into the e-CL-20(001) crystalline surface to build the PBX models. The cohesive energy densities (CEDs), elastic coefficients, isotropic mechanical properties (Young's moduli, bulk moduli, shear moduli, Poisson's ratio, Cauchy pressure and K/G) and initiation bond length distribution were studied. It turned out that the CEDs order was A1 < A4 < A3 < A2 < A. The mechanical properties of pure e-CL-20(001) were effectively improved by building PBX models. System A3 showed better comprehensive mechanical properties than the other three PBXs. A study on the initiation bond length distribution showed that the Lmax and Lave of N–NO2 increased with increasing temperature and they were related to the sensitivity of the explosives. The order of Lmax was A3 < A4 < A2 < A1 < A, which indicated that the PBXs owned lower sensitivity than system A. These studies are thought to provide guidance for further research on the application of GAP and its derivative polymers. Meanwhile, they are meaningful for the studies on e-CL-20-based PBXs.

The glass transition temperature (T g) and density of poly-(phthalazinone ether sulfone ketone) (PPESK A) were estimated by molecular dynamic (MD) simulation. A novel poly-(phthalazinone ether sulfone ketone) (PPESK B) was constructed by introducing nitrol and amini energetic groups into PPESK A, and T g and density were also simulated for PPESK B. The estimated T g values of PPESK A were very close to experimental results, while for PPESK B three estimated values differed by

The selected 18 energetic compounds were theoretically investigated by using the density functional theory (DFT) quantum mechanical code, DMol 3 , and the Hansen solubility parameters (HSPs) analyses. The results showed that 4-nitrotoluene, 4-nitrophenol, N , N ′-dimethyl- N , N ′-diphenylurea and N , N ′-diethyl- N , N ′-diphenylurea contain relatively electron-rich aromatic rings. Four satisfactory energetic precursors with electron-rich rings were quickly and effectively found by electrostatic potential (ESP) surfaces and HSPs analyses. The results also indicated that the absolute value of the lowest unoccupied molecular orbital (LUMO) of the energetic precursors with electron-rich rings often was less than 3.00 eV, and the absolute value of LUMO of the energetic precursors with electron deficient rings was often more than 3.00 eV. Additionally, we found that with at least two eutectic points was a prerequisite for two precursors to form a cocrystal.

In our study, liquid tin (Sn) was mixed with molten polyethylene using an internal mixer; the interfacial tension between the liquid Sn and molten polyethylene was measured using the deformed drop retraction method. The results showed that liquid Sn separated when the Sn content was higher than approximately 2 % by volume because of the interfacial tension of up to 167 mN/m and the 106-fold viscosity difference between the liquid Sn and the molten polyethylene. When Sn separation did not occur, the effects of the mixing time and rotary speed on the degree of mixing and the Sn particle size were analyzed using thermogravimetric analysis and scanning electron microscopy. The results showed that the effects of mixing time and rotary speed on the degree of mixing and Sn particle size can be combined as the impact of specific energy input. With increasing specific energy input, the degree of mixing initially increased and subsequently remained constant, while the Sn particle size initially decreased and subsequently remained constant. The refinement of the dispersed phase was completed with a low specific energy input, but the homogenization of the dispersed phase required a higher specific energy input to achieve completion, revealing the relationship between distributive mixing and dispersive mixing.

A new energetic polymer, poly(vinyl 2,4,6-trinitrophenylacetal)-co-poly(vinyl acetate azide) (PVTNP-co-PVAA), was synthesized by a two-step process involving initial chloroacetylation and subsequent azidation of poly(vinyl 2,4,6-trinitrophenylaceta). The synthesized polymers were characterized by elemental analysis, UV-Vis, ATR-FTIR, and 1H NMR techniques. The glass-transition temperature of PVTNP-co-PVAA was evaluated by differential scanning calorimetry (DSC), and the thermal stability of PVTNP-co-PVAA was tested by differential thermal analysis (DTA) and thermogravimetric analysis (TGA). DSC traces showed that PVTNP-co-PVAA had two glass-transition temperatures at −27.53 and 67.05 °C, respectively. DTA and TGA curves showed that the thermo-oxidative degradation of PVTNP-co-PVAA in air was a two-step reaction, and the percentage of degraded PVTNP-co-PVAA reached nearly 100% at 600 °C. Open image in new window

In an attempt to better understand the properties of energetic eutectic materials, the eutectic mixture of hydrazine nitrate (HN) and nitroguanidine (NQ) was prepared by a melt crystallization method. The melting temperature and fusion enthalpy of the pure components and the eutectic were determined using differential scanning calorimetry. The structure of the HN-NQ title compound was characterized by infrared spectroscopy (IR), X-ray diffraction (XRD), and scanning electron microscopy. Thermodynamic functions such as excess Gibb’s energy, excess enthalpy, and excess entropy of the title mixture were calculated using activity coefficient data. The intermolecular interactions of different molar ratios of the HN-NQ eutectic were determined by density functional theory (DFT) methods. The results of the excess thermodynamic functions and computer simulations indicate that the eutectic is not a mechanical mixture. IR spectroscopic and XRD studies confirm that there is some interaction between the components during the formation of the eutectic mixture. Moreover, the microstructure of the eutectic mixture at a molar ratio of 3 : 2 was more uniform than others, which was proved by DFT calculations. The Jackson’s roughness parameter was found to be greater than 2, suggesting a faceted, irregular morphology. These results could pave a way for further investigation of the energetic eutectic system aiming to supersede TNT.

2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is a high-energy nitramine explosive with high mechanical sensitivity. 2,4,6-trinitrotoluene (TNT) is insensitive but by no means a high performance explosive. To reveal the significant importance and smart-material functionality of the energetic-energetic co-crystals, the stability, mechanical and explosive properties TNT/CL-20 co-crystal, TNT crystal and CL-20 crystal were studied. Non-hydrogen bonded non-covalent interactions govern the structures of energetic-energetic co-crystals. However, it is very difficult to accurately calculate the non-covalent intermolecular interaction energies. In this paper, the local conformation and the intricate non-covalent interactions were effectively mapped and analyzed from the electron density (ρ) and its derivatives. The results show that the two components TNT and CL-20 are connected mainly by nitro-aromatic interactions, and nitro-nitro interactions. The steric interactions in TNT/CL-20 could not be confronted with the attractive interactions. Moreover, the scatter graph of TNT crystal reveals the reason why TNT is brittle. The detailed electrostatic potential analysis predicted that the detonation velocities (D) and impact sensitivity for the compounds both increase in the sequence of CL-20 > TNT/CL-20 co-crystal > TNT. Additionally, TNT/CL-20 co-crystal has better malleability than its pure components. This demonstrates the capacity and the feasibility of realizing explosive smart materials by co-crystallization, even if strong hydrogen bonding schemes are generally lacking in energetic materials.

Amorphous poly-para-xylylene (PPX) polymers were constructed using molecular mechanics (MM) and NVT+NPT-annealing methods. They provide the cut-off free volumes to absorb and transfer gas molecules. The corresponding sorption and diffusion properties were determined via Grand Canonical Monte Carlo (GCMC), NVT-Molecular Dynamics (MD) and cluster analysis methods. The results showed that temperature and pressure influence the sorption properties of gases obviously, but not to the diffusion coefficients of gases. Analyzing on the mean square displacement (MSD) data, this work finds that gases walk randomly through amorphous PPX polymers. The relative cluster permeability approaches to the experimental data.

A novel environmentally friendly octahedrally coordinated 2D polymeric complexes bis(1,5-diaminotetrazole) -dichlorozinc(II) (Zn(DAT)2Cl2) was first designed based on the the crystal data of bis(1,5-diaminotetrazole)- dichlorocopper(II) (Cu(DAT)2Cl2). Density functional theory (DFT) was used to predict the optimized geometries at TPSSTPSS/6-311G(d, p) level. Densities and detonation properties were evaluated using the electron cloud enclosed volume and VLW equation of state (VLW EOS), respectively. Calculation results show that the density of Zn(DAT)2Cl2 (2.117 g · cm−1) is a bit more than that of Cu(DAT)2Cl2 (2.106 g · cm−1). The calculated high positive heat of formation (HOF) predicts that the stabilities of the title compounds decrease in the order Zn(DAT)2Cl2 > Cu(DAT)2Cl2, which agrees with the result of bond dissociation energies (BDE). Even though they have the same molecule structures, their first scission steps are different. Furthermore, the title two compounds show good detonation velocities and pressures compared with that of bis-(5-nitro-2H-tetrazolato-N2) tetraamminecobalt(III) perchlorates (BNCP), and they are potential candidates for high-energy-density materials (HEDM).

Molecular mechanics (MM) and the gradually reduced size (GRS) techniques were used to construct the crystalline poly-p-xylylene (PPX) films, including PPX N, PPX C and PPX D. The corresponding chain-end area of crystalline PPX films provides enough free volumes for adsorbing and transferring gas molecules. Then, the permeable properties of gases were calculated using Grand Canonical Monte Carlo (GCMC), NVT-Molecular Dynamics (MD) and cluster analysis methods. The calculated diffusion coefficients are in the same order of magnitude over a range of temperatures and pressures. And there is no permeation property of gases in the inner part of the crystalline PPX films.

An investigation has been performed on the effect of the properties of solvent and anti-solvent, addition method of anti-solvent and crystallization temperature on the polymorphic transformation of HNIW precipitated from solution. The crystallization behavior of HNIW polymorphs were confirmed by powder X-ray diffraction (PXRD) and the polymorphic content was evaluated by Rietveld analysis. It was observed that the dipole moment of anti-solvent and the supersaturation were related to the variations in polymorphic form. The metastable form β always was precipitated initially in high polarity anti-solvent or in high supersaturation case, and then transformed to the stable form e by solution mediated process, which obeyed the Ostwald's rule of stages. A new acetone solvate was isolated in acetone solution, which was so unstable that it quickly desolated to obtain form β. The stability of the hydrate form α depends on the degree of hydration and hence the low hydration degree of form α precipitated from solution can transform to form e. Forms γ and e are enantiotropic relationship and the transformation temperature T c is associated with the solvent system. The investigation of the polymorphic transformation of HNIW contributes to the understanding of the crystallization mechanism and the preparing of the four pure forms of HNIW.

Aluminum enriched 1, 1-diamino-2, 2-dinitroethylene (Al-FOX-7) crystal, as a new high energy density material (HEDM), was designed and investigated using grand canonical monte carlo (GCMC), NVT+NPT-molecular dynamics (MD) and GGA-PBE-density functional theory (DFT) methods. The results show that, Al atoms break out H-bond of functional group of FOX-7 crystal, and form new Al-H and Al-O bonds. Their atomic content (x) influences the surface electronic states, friction sensitivities and cj detonation properties of Al-FOX-7 crystals. While x is 4 atoms, the crystal has the highest friction sensitivities and cj detonation temperatures, which are about 1.5 times to that of FOX-7 crystal.

The geometric conformation and electronic structure of bis-(5-nitro-2H-tetrazolato-N2)tetraammine cobalt(III) perchlorate and its Ni/Fe/Cu/Zn analogues are studied under the TPSS (Tao-Perdew-Staroverov-Scuseria) levels of density functional theory in order to throw light on the relationship between their energy gaps and impact sensitivity. While the perchlorate ions are coordinated with the copper cation, which is different from the other four compounds. NBO (Natural bond orbital) analyses indicated that the metal-ligand interaction in the Co complex is covalent, while the others are ionic. The analysis of the electrostatic potential demonstrated that the O atoms from the nitro-tetrazole ring and perchlorate were primarily negative, while the other atoms were positive. The study was also conducted to gain a better understanding of the correlation of the energy gap and impact sensitivity.

The spheroidizing of TATB (1,3,5-triamino-2,4,6-trinitrobenzene) can help to control preferred orientation and anisotropic expansion of TATB based PBXs, as well as to improve crystal quality, desensitizing efficiency, packing density, and even explosive energy. In this paper, TATB crystals with different morphology were obtained by high temperature recrystallization from anti-solvents. TATB was dispersed into DMSO and heated to dissolve. Water as an anti-solvent was added to the solution with different conrol parameters. We designed additional experiments to study the particular influence of these parameters. It was shown that the crystal morphology is strongly affected by the stirring rate and the amount of water added. The recrystallized TATB samples have similar thermal stability as starting TATB, but higher densities and purities, which indicates that the quality of TATB crystals was improved. By slowly adding an appropriate amount of water and cooling, regular crystals of TATB were obtained, which proves that water is a good morphology modifier for TATB.

A new energetic polymer, polyvinyl acetate azide (PVAA), was synthesized via a two-step process involving initial chloroacetylation and subsequent azidation of poly(vinyl alcohol) and was characterized by elemental analysis, UV–Vis, ATR–FTIR, 1H and 13C NMR techniques. The glass-transition temperature of PVAA was evaluated by DSC method and the thermal stability of PVAA was tested by DTA and TGA methods. The results indicate that PVAA shows single glass-transition temperature at 24.60 °C and exhibits good resistance to thermal decomposition up to 200 °C. Moreover, the sensitivity properties of PVAA were measured with the national military standard methods and the compatibilities of PVAA with the energetic components of TNT-based melt cast explosives were studied by using the non-isothermal DSC method. The results indicate that PVAA is an insensitive energetic polymer and can be safely used in melt cast explosives.

Density functional method was applied to study 1,5-diamino-1,2,3,4-tetrazole (DAT, CH4N6) in both gaseous and bulk states. The banding and electronic structures of crystalline have been investigated at DFT-B3LYP/ 6-311G** level of theory. Relaxed crystal structure compares well with experimental data. The light fluctuation of the frontier orbital, which is mainly formed by atomic orbital of N(4) (heterocycle), is the most reactive part of the molecule, which is in good agreement with the experimental results. The energy gap is 9.035 eV, which indicates that DAT is an insulator. The distribution of electrostatic potential is uniform, indicating DAT is insensitive. The charge density of the intermolecular regions in the plane is not overlaid, indicating that the intermolecular interaction between the neighboring molecules along this direction in the bulk is very weak. The overlap populations of N(1)N(2) bonds are much less than those of other bonds, therefore the N(1)N(2) bonds first rupture by external stimuli.