Crystal structure and explosive performance of a new CL-20/caprolactam cocrystal

An Optimized and Universal Protocol for the Synthesis of Morpholine-2,5-Diones from Natural Hydrophobic Amino Acids and Their Mixture

Morpholine-2,5-diones (MDs) are increasingly attractive compounds that can be produced using amino acid (AA) as a starting material. These compounds can undergo polymerization to produce biodegradable materials, namely, polydepsipeptides, that hold the potential to be used in medicinal applications. In this study, a simplified yet high-yield MD synthesis procedure was developed and applied to produce a range of MDs derived from hydrophobic AAs including Leu, Ile, Val, Phe, Asp(OBzl), Lys(Z), and Ser(tBu). Moreover, using a blend of hydrophobic amino acids (Leu, Ile, Val, and Phe), mixtures of MDs could be synthesized simultaneously. Finally, the polymerization of these MD mixtures was probed and proven successful. The concept investigated herein constitutes a novel path toward the valorization of protein-rich waste by producing renewable and biodegradable materials.

Temperature-dependent decomposition of the CL-20/MTNP cocrystal after phase separation

CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane)-based cocrystals are attractive energetic cocrystals with a potential for high energy and low sensitivity, which account for nearly one-third of energetic cocrystals. The applications of cocrystal explosives require in-depth understanding of their thermal kinetics behaviors. Although thermal kinetics of the decomposition of CL-20-based cocrystals having no melting point have been studied, relevant research of CL-20-based cocrystals having a melting point, which are also the most frequently observed type, is still rare. In this study, the CL-20/MTNP (1-methyl-3,4,5-trinitropyrazole) cocrystal was chosen as a typical CL-20-based cocrystal having a melting point to investigate its thermal kinetics behavior. The thermal decomposition of CL-20/MTNP was identified to be a typical heterogeneous reaction with phase separation before decomposition. Due to the presence of intermolecular hydrogen bonds between CL-20 and molten MTNP after phase separation, the thermal decomposition behavior of CL-20/MTNP was strongly temperature-dependent. The complex decomposition reaction was separated into its three constituent pathways to simplify the kinetic analysis. On the basis of in-depth understanding of the decomposition process, the best functions of mechanism and kinetic parameters for each process of CL-20/MTNP decomposition were obtained using the model-fitting method. Finally, important thermal safety indicators, such as TMRad and SADT were simulated by combining the established kinetic models. This study provides further insights into the entire reaction process of the CL-20/MTNP cocrystal and would help in its better applications.

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.

Isothermal structural evolution of CL-20/HMX cocrystals under slow roasting at 190 °C

As a new type of energetic material, cocrystal explosives demonstrate many excellent properties, such as high energy density and low sensitivity, due to the interaction between the molecules of the two components. The known decomposition temperature is 235 °C for CL-20/HMX cocrystals at a faster heating rate. CL-20 molecules could separate from the cocrystal matrix and decompose at a higher temperature, much lower than the decomposition temperature. The current work provided deep insight into the isothermal structural evolution of CL-20/HMX cocrystals with slow roasting at 190 °C. We found that the initial decomposition originates from separating CL-20 molecules from the surface along the (010) plane of the cocrystals. The gas products, such as NO₂ and NO, escape from the largest exposed surface of the (010) plane and generates microbubbles and microholes. At the same time, the residual HMX molecules form δ-phase HMX crystals and shrink the volume by 72%. By increasing the time held at 190 °C, the decomposition of CL-20 molecules and recrystallization of the residual HMX molecules form a gully-like structure on the (010) plane of the CL-20/HMX cocrystal. After a long time at 190 °C, the CL-20 component completely decomposes, and all HMX molecules recrystallize in the δ-HMX form. The interaction between HMX and CL-20 molecules makes the decomposition rate of the CL-20/HMX cocrystal much slower than that of the CL-20 pure crystal with a similar decomposition activation energy during isothermal heating. This work can help to deeply understand the safety of CL-20/HMX cocrystal explosives at a temperature lower than the recognized decomposition temperature.

"Thermal escape" of MTNP: the phase separation of CL-20/MTNP cocrystals under long-term heating

High-energy, low-sensitivity energetic cocrystals are one successful application of the supramolecular strategy. The practical application of cocrystal explosives requires an in-depth understanding of the stability of their crystal phase structure under long-term heating, but relevant research is rare. In this study, the CL-20/MTNP (2, 4, 6, 8, 10, 12-hexanitrohexaazaisowurtzitane/1-methyl-3,4,5-trinitropyrazole) cocrystal was selected as a representative cocrystal explosive to investigate its crystal phase structure stability under long-term heating. The phase separation of the CL-20/MTNP cocrystal was observed for the first time. It was revealed that the MTNP molecules at crystal defects first underwent molecular rotation, which weakened interactions between CL-20 and MTNP molecules. Then, the MTNP molecules diffused along channels surrounded by CL-20 molecules to the crystal surface and escaped to generate γ-CL-20. We call this process the "thermal escape" of MTNP, whose effect on the safety performance of the CL-20/MTNP cocrystal was studied by comparing the mechanical sensitivity of samples with different degrees of thermal escape. The mechanical sensitivity of the CL-20/MTNP cocrystal did not greatly change during the induction period, but it increased upon the loss of MTNP. Moreover, the thermal escape kinetics for the two stages were obtained to prevent or control their thermal escape. The prediction of the kinetics confirmed the validity of the kinetic analysis. This study promotes the performance evaluation and application of CL-20/MTNP cocrystals and also provides a new perspective in the investigation of cocrystal explosives.

Study on the effect of solvent on cocrystallization of CL-20 and HMX through theoretical calculations and experiments

Cocrystallization is a helpful method for explosives design. However, lack of understanding of the cocrystallization mechanism leads to inefficiency in cocrystal preparation. Therefore, studying the effects of solvent on cocrystal is of great importance for the efficient application of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20). In this paper, the effect of solvent on cocrystallization is investigated by the CL-20/HMX cocrystal/solvent cluster model, the CL-20/HMX/solvent mixture model, the CL-20/HMX cocrystal/solvent interface model combined with quantum chemistry and molecular dynamic methods. The authors find that the hydrogen bond between CL-20 and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) is the strongest and the binding energy of cocrystal and solvent molecules is the weakest in ethyl acetate (EA) solvent, indicating that CL-20 and HMX tend to be combined together and there is less hindrance by solvent molecules. Analysis of the CL-20/HMX/solvent mixture and mass density distribution studies show that the solvent effect has a great influence on the crystal faces and the cocrystallization rate of CL-20 and HMX is the highest in EA solvent. The XRD and SEM characterization results are consistent with the theoretical calculations. The present work on the effects of solvent on CL-20/HMX cocrystals is beneficial for understanding the mechanism of the growth of energetic cocrystal materials. It is helpful in selecting more suitable theoretical and experimental conditions and makes access to excellent cocrystals more efficient.

Cocrystallization is a helpful method for explosives design. Studying the effects of solvent on cocrystal is of great importance for the efficient application of CL-20/HMX cocrystal.

A novel energetic cocrystal composed of CL-20 and 1-methyl-2,4,5-trinitroimidazole with high energy and low sensitivity

A cocrystal explosive comprising 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and 1-methyl-2,4,5-trinitroimidazole (MTNI) (molar ratio, 1:1) was synthesized. The structure of the cocrystal was characterized by single-crystal X-ray diffraction. Its structure was further determined by powder X-ray diffraction, infrared spectroscopy and differential scanning calorimetry which showed that its morphology was different from the morphology of the mechanical mixture of two raw materials. The decomposition temperature of the cocrystal is lower than that of CL-20 and MTNI. The calculated detonation performance is slightly lower than that of HMX, but the cocrystal has excellent sensitivity performance relative to that of CL-20, even lower than that of RDX. These features make this cocrystal ideal to be used in applications with low-sensitivity requirements.

Study on the Cocrystallization Mechanism of CL-20/HMX in a Propellant Aging Process through Theoretical Calculations and Experiments

Energetic materials undergo physical and chemical aging due to environmental effects, resulting in the degradation of safety and detonation performances. Therefore, studying the aging performance of energetic materials is of great importance for the efficient application of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20)-based solid propellants. In this paper, XRD and FTIR of the CL-20-based propellant and CL-20/1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX)-based propellant samples showed CL-20/HMX cocrystal formation according to appearance of new peaks. SEM and EDS analyses showed that pores and dehumidification in the propellant occurred with the cocrystallization of CL-20 and HMX during the aging process. Furthermore, molecular dynamics simulation was used to predict the crystal transformation of the CL-20- and HMX-based propellant under a long-term storage process. The stability of ε-CL-20 was obtained by analyzing the crystal transformation rate. The binding energy, radial distribution function between CL-20 and HMX, as well as mechanical properties of the CL-20/HMX cocrystal and the mixture were calculated to reveal the stronger binding between CL-20 and HMX in the cocrystal. Meanwhile, the inducer effect of a nitrate ester during the cocrystallization process was analyzed. The theoretical calculation shows that during aging, ε-CL-20 tends to exist stably, while CL-20/HMX tends to form cocrystals because of the strong bond. The present work on the transformation and cocrystallization of CL-20 and HMX during long-term storage is beneficial for understanding the degradation mechanism of the propellant performances, facilitating safe storage and life evaluation of propellants.

Four Novel Pharmaceutical Cocrystals of Oxyresveratrol, Including a 2 : 3 Cocrystal with Betaine

Cocrystal engineering can alter the physicochemical properties of a drug and generate a superior drug candidate for formulation design. Oxyresveratrol (ORV) exhibits a poor solubility in aqueous environments, thereby resulting in a poor bioavailability. Extensive cocrystal screening of ORV with 67 cocrystal formers (coformers) bearing various functional groups was therefore conducted using grinding, liquid-assisted grinding, solvent evaporation, and slurry methods. Six cocrystals (ORV with betaine (BTN), L-proline (PRL), isonicotinamide, nicotinamide, urea, and ethyl maltol) were found, including four novel cocrystals. Powder X-ray diffraction, low frequency Raman spectroscopy, and thermal analysis revealed unique crystal forms in all obtained samples. Conventional Raman and infrared data differentiated the cocrystals by the presence or absence of a hydrogen bond interacting with the aromatic ring of ORV. The crystal structures were then elucidated by single-crystal X-ray diffraction. Two new cocrystals consisting of ORV : BTN (2 : 3) and ORV : PRL : H₂O (1 : 2 : 1) were identified, and their crystal structures were solved. We report novel cocrystalline solids of ORV with improved aqueous solubilities and the unique cage-like crystal structures.

HMX/NMP cocrystal explosive: first-principles calculations

The band structure, total density of states, and atomic orbit projected density of states analysis were performed to investigate HMX/NMP cocrystal by using the first-principles calculations. Results show that the HMX/NMP cocrystal is equipped with a direct band gap and the interactions between HMX and NMP molecules are rather weak. The O orbits hybridize with H orbits, and the parts of charge transform from H to O atoms by analyzing the DOS. The HMX/NMP cocrystal possesses three types of intermolecular interactions between HMX and NMP; these interactions and the arrangement of two molecules in the structure are the main reasons for the low sensitivity of the cocrystal. The C-H…O type hydrogen bond is the key role in forming the structure, and the strength of the hydrogen bond interaction for C-H…O-N is higher than that of C-H…O-C.

Engineering cocrystals of Paliperidone with enhanced solubility and dissolution characteristics

In the present study, co-crystals (CCs) of Paliperidone (PPD) with coformers like benzoic acid (BA) and P-amino benzoic acid (PABA) were synthesized and characterized to improve the physicochemical properties and dissolution rate. CCs were prepared by the solvent evaporation (SE) technique and were compared with the products formed by neat grinding (NG) and liquid assisted grinding (LAG) in their enhancement of solubility. The formation of CCs was confirmed by the IR spectroscopy, powder X-ray diffraction and thermal analysis methods. The saturation solubility studies indicate that the aqueous solubility of PPD-BA and PPD-PABA CCs was significantly improved to 1.343±0.162mg/ml and 1.964±0.452mg/ml, respectively, in comparison with the PPD solubility of 0.473mg/ml. This increase in solubility is 2.83-and 3.09-fold, respectively. PPD exhibited a poor dissolution of 37.8% in 60min, while the dissolution of the CCs improved tremendously to 96.07% and 89.65% in 60min. CCs of PPD with BA and PABA present a novel approach to overcome the solubility challenges of poorly water-soluble drug PPD.

Experimental and Theoretical Study on the Stability of CL-20-Based Host-Guest Energetic Materials

CL-20-based host-guest complexes are promising energetic materials, which are prepared by embedding small molecules into the crystal lattice cavity of anhydrous CL-20. The structure, interaction, stability, and detonation performance of a series of host-guest complexes were investigated by the combination method of density functional theory and experiment. Both the crystal structure of α-CL-20/H₂O and α-CL-20/N₂O revealed by powder X-ray diffraction and the thermal stability order of α-CL-20/N₂O, α-CL-20/CO₂, α-CL-20/H₂O, and α-CL-20/H₂O₂ measured using a differential scanning calorimeter show excellent accordance between experimental results and simulative predication. Thus, the reliability of the calculation method can be judged by the result of this comparison. The stability of different host-guest structures was compared under vacuum, and the influence of intermolecular interactions on the structural stability was discussed. In view of the various factors affecting the performance of high-energy explosives, such as detonation performance, thermal stability, and density, we conclude that α-CL-20/O₃ could be regarded as a potential target high-energetic compound. On the basis of the above results, this calculation method can provide a theoretical basis for the preparation of CL-20-based host-guest energetic compounds.

Enhancing chemical stability of tetranitro biimidazole-based energetic materials through co-crystallization

Co-crystallization technology was employed as a way of solving two problems hampering the usefulness of 4,4′,5,5′-tetranitro-2,2′biimidazole (TNBI) as a viable energetic material, namely hygroscopicity and corrosiveness (high acidity). Co-crystal screening was carried out with 15 co-formers containing nitrogen or oxygen as the primary hydrogen-bond acceptor site. Formation of co-crystals was confirmed by IR spectroscopy and DSC, and suitable co-crystals were then analysed via single-crystal X-ray diffraction. In each case, the formation of a co-crystal was driven by the formation of multiple N–H···N or N–H···O hydrogen bonds between TNBI and the co-former. The N-oxide based acceptors produce better energetic materials due to a more optimal oxygen balance. Hygroscopicity evaluations and corrosion tests revealed that the unavailability of N–H protons in the co-crystals of TNBI reduce hygroscopicity and suppress the chemical acidity of the free parent compound thereby making it substantially easier to handle, store, and transport.

Comparative investigation on the thermostability, sensitivity, and mechanical performance of RDX/HMX energetic cocrystal and its mixture

Molecular mechanics (MM) and molecular dynamics (MD) simulation method were applied to explore the impact of temperature (220-380 K) on the thermostability, sensitivity, and mechanical performance of RDX (1,3,5-trinitro-1,3,5-triazacyco-hexane)/HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) energetic cocrystal and mixture models. The mechanical property, the maximum trigger bond length ([Formula: see text]), binding energy, and cohesive energy density (CED) of the pure RDX, β-HMX crystal, the cocrystal, and mixture models were acquired and compared. The results manifest that temperature has an important impact on the binding capacity between the components of the cocrystal and mixture. The binding energies decrease as the temperature rises, and the cocrystal has larger values than those of mixture. For all the models, the [Formula: see text] increases and the CEDs decrease with the rising temperature, implying that the sensitivity of the explosives increases, while the [Formula: see text] values of the cocrystal are smaller than those of HMX and the CED values are between those of RDX and β-HMX, indicating that the sensitivity has been enhanced through co-crystallization. As the temperature increases, the shear modulus (G), bulk modulus (K), and tensile modulus (E) values of all models have an evident downtrend. Simultaneously, G, K, and E values of the cocrystal model are less than those of RDX and β-HMX, while the K/G ratio and Cauchy pressure (C₁₂-C₄₄) are larger, signifying that co-crystallization can weaken the brittleness and enhance the ductility of the pure crystals. Compared with the mixture, the cocrystal has better ductility and stability.

Theoretical studies on the structure and properties of DAT/BTNAT cocrystal under high pressure

The structural, electronic, and absorption properties of 3,5-diamino-1H-1,2,4-triazole (DAT) and 5,5′-bis(trinitromethyl)-3,3′-azo-1H-1,2,4-triazole (BTNAT) cocrystal under hydrostatic compression of 0–100 GPa were investigated by using periodic density functional theory with dispersion correction (DFT-D). The results indicate that a structural transformation occurred at 25 GPa. The structural transformation makes the positions of the molecules rearrange in the cocrystal and improves the stability and planarity. An analysis of the band gap and density of states indicates that the DAT/BTNAT cocrystal becomes more sensitive under compression. The absorption spectra illustrate that the DAT/BTNAT cocrystal has relatively high optical activity with the increasing pressure. Our work may offer some valuable information for understanding the behavior of energetic cocrystals under high pressure.

Theoretical calculation into the effect of molar ratio on the structures, stability, mechanical properties and detonation performance of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane/ 1,3,5-trinitro-1,3,5-triazacyco-hexane cocrystal

Molecular dynamics (MD) simulation was conducted to research the effect of molar ratio on the thermal stability, mechanical properties, and detonation performance of HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane)/RDX (1,3,5-trinitro-1,3,5-triazacyco-hexane) cocrystal explosive at ambient condition. The binding energy, mechanical properties, and the detonation parameters of the pure β-HMX, RDX crystal, and the cocrystal models were got and contrasted. The results demonstrate that molar ratio has a great influence on the properties of the cocrystal system. The binding energy of the cocrystals has the maximum values at the 1:1 molar ratio, indicating that the stability of HMX/RDX(1:1) cocrystal is the best and HMX and RDX may prefer to cocrystallizing at 1:1 molar ratio. What's more, the tensile modulus (E) and shear modulus (G) of the HMX/RDX(1:1) cocrystals have the minimum value, while the C₁₂-C₄₄ and K/G have the maximum value, implying that the cocrystal at 1:1 molar ratio has the best mechanical properties. Simultaneously, the E, K, and G of the cocrystals are all smaller than those of β-HMX's and generally larger than those RDX's, while the Cauchy pressure (C₁₂-C₄₄) and K/G ratio were greater, demonstrating that cocrystallizing can improve the brittleness and enhance the ductility. The detonation velocity (D) and detonation pressure (P) decrease with the rising RDX content, while the properties are still superior to the pure RDX crystal; thus, the energy properties of the cocrystal are still excellent. In a word, HMX/RDX cocrystal at 1:1 molar ratio has the best thermal stability, mechanical properties, and the excellent energetic performance.

Predicting Value of Binding Constants of Organic Ligands to Beta-Cyclodextrin: Application of MARSplines and Descriptors Encoded in SMILES String

The quantitative structure–activity relationship (QSPR) model was formulated to quantify values of the binding constant (lnK) of a series of ligands to beta–cyclodextrin (β-CD). For this purpose, the multivariate adaptive regression splines (MARSplines) methodology was adopted with molecular descriptors derived from the simplified molecular input line entry specification (SMILES) strings. This approach allows discovery of regression equations consisting of new non-linear components (basis functions) being combinations of molecular descriptors. The model was subjected to the standard internal and external validation procedures, which indicated its high predictive power. The appearance of polarity-related descriptors, such as XlogP, confirms the hydrophobic nature of the cyclodextrin cavity. The model can be used for predicting the affinity of new ligands to β-CD. However, a non-standard application was also proposed for classification into Biopharmaceutical Classification System (BCS) drug types. It was found that a single parameter, which is the estimated value of lnK, is sufficient to distinguish highly permeable drugs (BCS class I and II) from low permeable ones (BCS class II and IV). In general, it was found that drugs of the former group exhibit higher affinity to β-CD then the latter group (class III and IV).

Design, preparation, characterization and formation mechanism of a novel kinetic CL-20-based cocrystal

2,4,6,8,10,12-Hexanitrohexaazaisowurtzitane (CL-20)-based cocrystals have gained increasing attention as a means of obtaining insensitive high explosives. However, the design of ideal candidates for these cocrystals remains difficult. This work compares the crystal energies of the CL-20-dinitrobenzene (DNB) and CL-20-2,4,6-trinitrotoluene (TNT) cocrystals with those of the respective pure coformers. The results indicate that the cocrystal formation is driven by the differences in the energies of the cocrystals and the coformers. Furthermore, analysis via Hirshfeld surfaces and two-dimensional fingerprint plots confirms that the O...O, O...H, O...N and C...O interactions were the main force for stabilizing the CL-20-based cocrystal structure. Based on these findings, a novel energetic-energetic cocrystal of CL-20-2,4,6-trinitrophenol (TNP) was designed and prepared by means of a rapid method for solvent removal. The crystal structure was investigated via powder X-ray diffraction methods, solid-state nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy. The results revealed that the O-H...O hydrogen bonding interaction between the phenolic hydroxyl group of TNP and nitro groups of CL-20, as well as nitro...π, nitro...nitro and O_NO2...π(N)_NO2 interactions, based on the benzene ring and nitro groups, are the main interactions occurring in the cocrystal.

Theoretical investigations on structures, stability, energetic performance, sensitivity, and mechanical properties of CL-20/TNT/HMX cocrystal explosives by molecular dynamics simulation

In this article, the CL-20, TNT, HMX, CL-20/TNT, CL-20/HMX and different CL-20/TNT/HMX cocrystal models were established. Molecular dynamics method was selected to optimize the structures, predict the stability, sensitivity, energetic performance, and mechanical properties of cocrystal models. The binding energy, trigger bond length, trigger bond energy, cohesive energy density, detonation parameters, and mechanical properties of each crystal model were obtained. The influences of co-crystallization and molar ratios on performances of cocrystal explosives were investigated and evaluated. The results show that the CL-20/TNT/HMX cocrystal explosive with a molar ratio of 3:1:2 or 3:1:3 had larger binding energy and better stability, i.e., CL-20/TNT/HMX cocrystal explosive was more likely to be formed with these molar ratios. The cocrystal explosive had shorter maximal trigger bond length, but larger trigger bond energy and cohesive energy density than CL-20, namely, the cocrystal explosive had lower mechanical sensitivity and better safety than CL-20 and the safety of cocrystal model was effectively improved. The cocrystal model with a molar ratio of 3:1:2 had the best safety. The energetic performance of the cocrystal explosive with a molar ratio of 3:1:1, 3:1:2, or 3:1:3 was the best. These CL-20/TNT/HMX cocrystal models exhibited better and more desirable mechanical properties. In a word, the cocrystal model with molar ratio of 3:1:2 exhibited the most superior properties and was a novel and potential high-energy-density compound. This paper could provide practical helpful guidance and theoretical support to better understand co-crystallization mechanisms and design novel energetic cocrystal explosives.

Theoretical investigations on the structures and properties of CL-20/TNT cocrystal and its defective models by molecular dynamics simulation

"Perfect" and defective models of CL-20/TNT cocrystal explosive were established. Molecular dynamics methods were introduced to determine the structures and predict the comprehensive performances, including stabilities, sensitivity, energy density and mechanical properties, of the different models. The influences of crystal defects on the properties of these explosives were investigated and evaluated. The results show that, compared with the "perfect" model, the rigidity and toughness of defective models are decreased, while the ductility, tenacity and plastic properties are enhanced. The binding energies, interaction energy of the trigger bond, and the cohesive energy density of defective crystals declined, thus implying that stabilities are weakened, the explosive molecule is activated, trigger bond strength is diminished and safety is worsened. Detonation performance showed that, owing to the influence of crystal defects, the density is lessened, detonation pressure and detonation velocity are also declined, i.e., the power of defective explosive is decreased. In a word, the crystal defects may have a favorable effect on the mechanical properties, but have a disadvantageous influence on sensitivity, stability and energy density of CL-20/TNT cocrystal explosive. The results could provide theoretical guidance and practical instructions to estimate the properties of defective crystal models.

Theoretical investigation of the structures and properties of CL-20/DNB cocrystal and associated PBXs by molecular dynamics simulation

In this work, a CL-20/DNB cocrystal explosive model was established and six different kinds of fluoropolymers, i.e., PVDF, PCTFE, F₂₃₁₁, F₂₃₁₂, F₂₃₁₃ and F₂₃₁₄ were added into the (1 0 0), (0 1 0), (0 0 1) crystal orientations to obtain the corresponding polymer bonded explosives (PBXs). The influence of fluoropolymers on PBX properties (energetic property, stability and mechanical properties) was investigated and evaluated using molecular dynamics (MD) methods. The results reveal a decrease in engineering moduli, an increase in Cauchy pressure (i.e., rigidity and stiffness is lessened), and an increase in plastic properties and ductility, thus indicating that the fluoropolymers have a beneficial influence on the mechanical properties of PBXs. Of all the PBXs models tested, the mechanical properties of CL-20/DNB/F₂₃₁₁ were the best. Binding energies show that CL-20/DNB/F₂₃₁₁ has the highest intermolecular interaction energy and best compatibility and stability. Therefore, F₂₃₁₁ is the most suitable fluoropolymer for PBXs. The mechanical properties and binding energies of the three crystal orientations vary in the order (0 1 0) > (0 0 1) > (1 0 0), i.e., the mechanical properties of the (0 1 0) crystal orientation are best, and this is the most stable crystal orientation. Detonation performance results show that the density and detonation parameters of PBXs are lower than those of the pure CL-20 and CL-20/DNB cocrystal explosive. The power and energetic performance of PBXs are thus weakened; however, these PBXs still have excellent detonation performance and are very promising. The results and conclusions provide some helpful guidance and novel instructions for the design and manufacture of PBXs.

Optimizing the oxygen balance by changing the A-site cations in molecular perovskite high-energetic materials

Two new members of molecular perovskite high-energetic materials exhibit optimized oxygen balances by changing the A-site cations.

Electronic and reactivity characteristics of CL-20 covalent chains and networks: a density functional theory study

The low-dimensional nanostructures built with CL-20 units were studied in order to investigate the possibility of creating covalent CL-20 crystals.

Novel insensitive energetic-cocrystal-based BTO with good comprehensive properties

Combining a layer construction strategy with cocrystallization techniques, we designed and prepared a structurally unusual 1H,1′H-5,5′-bistetrazole-1,1′-diolate (BTO) based energetic cocrystal, which we also confirmed by single-crystal X-ray diffraction and powder-crystal X-ray diffraction. The obtained cocrystal crystallizes in a triclinic system, P-1 space group, with a density of 1.72 g cm⁻³. The properties including the thermal stability, sensitivity and detonation performance of the cocrystal were analyzed in detail. In addition, the thermal decomposition behavior of the cocrystal was studied by differential calorimetry and thermogravimetry tandem infrared spectroscopy. The results indicated that the cocrystal exhibits strong resistance to thermal decomposition up to 535.6 K. The cocrystal also demonstrates a sensitivity of >50 J. Moreover, its formation enthalpy was estimated to be 2312.0 kJ mol⁻¹, whereas its detonation velocity and detonation pressure were predicted to be 8.213 km s⁻¹ and 29.1 GPa, respectively, by applying K–J equations. Therefore, as expected, the obtained cocrystal shows a good comprehensive performance, which proves that a high degree of layer-by-layer stacking is essential for the structural density, thermal stability and sensitivity.

Combining a layer construction strategy with cocrystallization techniques, we designed and prepared an unusual energetic cocrystal, which confirmed by single-crystal X-ray diffraction.

Direct insight into the formation driving force, sensitivity and detonation performance of the observed CL-20-based energetic cocrystals

This work elucidated the underlying mechanism of the dramatic and divergent physicochemical properties of CL-20-based energetic cocrystals.

Theoretical insight into the cocrystal explosive of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20)/1-Methyl-4,5-dinitro-1H-imidazole (MDNI)

Cocrystal explosive is getting more and more attention in high energy density material field. Different molar ratios of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20)/1-Methyl-4,5-dinitro-1H-imidazole (MDNI) cocrystal were studied by molecular dynamics (MD) simulation and quantum-chemical density functional theory (DFT) calculation. Binding energy of CL-20/MDNI cocrystal and radial distribution function (RDF) were used to estimate the interaction. Mechanical properties were calculated to predict the elasticity and ductility. The length and bond dissociation energy of trigger bond, surface electrostatic potentials (ESP) of CL-20/MDNI framework were calculated at B3LYP/6-311[Formula: see text]G(d,p) level. The results indicate that CL-20/MDNI cocrystal explosive might have better mechanical properties and stability in a molar ratio 3:2. The N–NO2 bond becomes stronger upon the formation of intermolecular H-bonding interaction. The surface electrostatic potential further confirms that the sensitivity decreases in cocrystal explosive in comparison with that in isolated CL-20. The oxygen balance (OB), heat of detonation ([Formula: see text], detonation velocity ([Formula: see text] and detonation pressure ([Formula: see text] of CL-20/MDNI suggest that the CL-20/MDNI cocrystal possesses excellent detonation performance and low sensitivity.

Theoretical insights into the effects of molar ratios on stabilities, mechanical properties, and detonation performance of CL-20/HMX cocrystal explosives by molecular dynamics simulation

To research and estimate the effects of molar ratios on structures, stabilities, mechanical properties, and detonation properties of CL-20/HMX cocrystal explosive, the CL-20/HMX cocrystal explosive models with different molar ratios were established in Materials Studio (MS). The crystal parameters, structures, stabilities, mechanical properties, and some detonation parameters of different cocrystal explosives were obtained and compared. The molecular dynamics (MD) simulation results illustrate that the molar ratios of CL-20/HMX have a direct influence on the comprehensive performance of cocrystal explosive. The hardness and rigidity of the 1:1 cocrystal explosive was the poorest, while the plastic property and ductibility were the best, thus implying that the explosive has the best mechanical properties. Besides, it has the highest binding energy, so the stability and compatibility is the best. The cocrystal explosive has better detonation performance than HMX. In a word, the 1:1 cocrystal explosive is worth more attention and further research. This paper could offer some theoretical instructions and technological support, which could help in the design of the CL-20 cocrystal explosive.

Preparation and characterization of an ultrafine HMX/NQ co-crystal by vacuum freeze drying method

In this paper a new energetic co-crystal consisting of 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX) and nitroguanidine (NQ) was prepared using a vacuum freeze drying method.

Molecular dynamic simulations on TKX-50/HMX cocrystal

TKX-50/HMX cocrystal model was established and calculated using PCFF force field by molecular dynamics simulations.

Theoretical insights into the stabilities, detonation performance, and electrostatic potentials of cocrystals containing α- or β-HMX and TATB, FOX-7, NTO, or DMF in various molar ratios

A molecular dynamics method was employed to study the binding energies associated with the cocrystallization (at selected crystal planes) of either 1,3,5-triamino-2,4,6-trinitro-benzene (TATB), 1,1-diamino-2,2-dinitroethylene, 3-nitro-1,2,4-triazol-5-one (TATB, FOX-7, and NTO, respectively, all of which are explosives), or N,N-dimethylformamide (DMF, a nonenergetic solvent) in various molar ratios with 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane in its α and β conformations (α-HMX and β-HMX, respectively). The results showed that the cocrystals with low molar ratios (2:1, 1:1, 1:2, and 1:3) were the most stable. The binding energies of HMX/NTO and HMX/DMF were larger than those of HMX/TATB and HMX/FOX-7. According to the calculated stabilities, HMX prefers to adopt its α form in HMX/TATB and its β form in HMX/NTO, whereas the two forms coexist in HMX/FOX-7. For HMX/TATB, HMX/NTO, and α-HMX/FOX-7, increasing the proportion of the cocrystal component with the highest detonation heat (HMX in the first two cases, FOX-7 in the latter) increases the detonation heat, velocity, and pressure of the cocrystal. However, increasing the proportion of the component with the highest detonation heat in β-HMX/FOX-7 and γ-CL-20/FOX-7 increases the detonation heat of the cocrystal but decreases its detonation velocity. An investigation of the surface electrostatic potential revealed how the sensitivity changes upon cocrystal formation. Graphical Abstract Surface electrostatic potential of HMX/TATB.