Smart Host-Guest Energetic Material Constructed by Stabilizing Energetic Fuel Hydroxylamine in Lattice Cavity of 2,4,6,8,10,12-Hexanitrohexaazaisowurtzitane Significantly Enhanced the Detonation, Safety, Propulsion, and Combustion Performances

Self-Template Evolution Toward Hierarchically Hollow Spherulites of Energetic Materials for Safety Control and Combustion Enhancement

The hierarchical hollow structure can endow functional materials with concerning performances, whereas its rational design remains challenging, especially for organic molecules. Herein, a novel strategy of self-template evolution is presented to construct hollow spherulites (HSs) for energetic organic materials with controllable safety and enhanced combustion, utilizing the mechanism of pseudomorphic replacement coupled with Ostwald ripening. Specifically, the spherulites of thermodynamically metastable β-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (β-CL-20) as the self-template spontaneously evolves into the HSs of CL-20-based inclusion compounds in solution, during which the dissolution of β-CL-20 and the crystallization of CL-20-based inclusion compounds are spatiotemporally correlated, enabling pseudomorphic replacement preserving the spherulitic structure, and cavities are formed inside via Ostwald ripening. Moreover, the conversion rates and the mediating solvent cause different locations of cavities, with two cases exhibited. The hollow-core spherulites of CL-20-formic acid exhibit controllable safety through manipulating micro-/nanostructures, and the hollow-spoke spherulites of CL-20-CO2 can be the efficient carrier to composite with oxidants, enhancing combustion with increases of 23.2% in pressure duration effect, 9.8% in peak pressure, and 3.3% in pressurization rate. This work offers a novel route to construct hierarchical hollow energetic crystals with enhanced performance and puts insight into the design of hierarchical hollow crystals for broad material systems.

Construction of Adaptive Deformation Block: Rational Molecular Editing of the N-Rich Host Molecule to Remove Water from the Energetic Hydrogen-Bonded Organic Frameworks

Energetic hydrogen-bonded organic frameworks (E-HOFs), as a type of energetic material, spark fresh vitality to the creation of high energy density materials (HEDMs). However, E-HOFs containing cations and anions face challenges such as reduced energy density due to the inclusion of crystal water. In this work, the modification of amino groups in N-rich organic units could form a smart building block of hydrogen-bonded frameworks capable of changing the volume of the void space in the molecule through adaptive deformation of E-MOF blocks, thus enabling the replacement of water. Based on the above strategy, we report an interesting example of a series of hydrogen-bonded organic frameworks (E-HOF 2a and 3a) synthesized using a facile method. The crystal structure data of all of the compounds were also obtained in this work. Anhydrous 2a and 3a exhibit higher density, good thermal stability, and low mechanical sensitivity. The strategy of covalent bond modification for the host molecules of energetic frameworks shows enormous potential in eliminating the crystalline H2O of hydration and exploring high energy density materials.

Can a heavy trinitromethyl group always result in a higher density?

Density is an important property of energetic materials and is believed to increase with the addition of heavy trinitromethyl groups, as shown in previous literature. However, this study determined that the introduction of these groups produced a decrease in density, as evidenced by the lower density of 1-trinitromethyl-4-amino-3,5-dinitropyrazole ((TN-116), 1.899 g cm^-3) compared to that of its precursor (4-amino-3,5-dinitropyrazole (LLM-116), 1.900 g cm^-3). Mechanistic studies indicated that the reduced density was due to the significantly weaker H-bonding and π-π interactions of TN-116, which produced looser stacking compared to that of LLM-116.

Effects of Different Guests on Pyrolysis Mechanism of α-CL-20/Guest at High Temperatures by Reactive Molecular Dynamics Simulations at High Temperatures

The host-guest inclusion strategy has the potential to surpass the limitations of energy density and suboptimal performances of single explosives. The guest molecules can not only enhance the detonation performance of host explosives but also can enhance their stability. Therefore, a deep analysis of the role of guest influence on the pyrolysis decomposition of the host-guest explosive is necessary. The whole decomposition reaction stage of CL-20/H₂O, CL-20/CO₂, CL-20/N₂O, CL-20/NH₂OH was calculated by ReaxFF-MD. The incorporation of CO₂, N₂O and NH₂OH significantly increase the energy levels of CL-20. However, different guests have little influence on the initial decomposition paths of CL-20. The E_a1 and E_a2 values of CL-20/CO₂, CL-20/N₂O, CL-20/NH₂OH systems are higher than the CL-20/H₂O system. Clearly, incorporation of CO₂, N₂O, NH₂OH can inhibit the initial decomposition and intermediate decomposition stage of CL-20/H₂O. Guest molecules become heavily involved in the reaction and influence on the reaction rates. k₁ of CL-20/N₂O and CL-20/NH₂OH systems are significantly larger than that of CL-20/H₂O at high temperatures. k₁ of CL-20/CO₂ system is very complex, which can be affected deeply by temperatures. k₂ of the CL-20/CO₂, CL-20/N₂O systems is significantly smaller than that of CL-20/H₂O at high temperatures. k₂ of CL-20/NH₂OH system shows little difference at high temperatures. For the CL-20/CO₂ system, the k₃ value of CO₂ is slightly higher than that for CL-20/H₂O, CL-20/N₂O, CL-20/NH₂OH systems, while the k₃ values of N₂ and H₂O are slightly smaller than that for the CL-20/H₂O, CL-20/N₂O, CL-20/NH₂OH systems. For the CL-20/N₂O system, the k₃ value of CO₂ is slightly smaller than that for CL-20/H₂O, CL-20/CO₂, CL-20/NH₂OH systems. For the CL-20/NH₂OH system, the k₃ value of H₂O is slightly larger than that for CL-20/H₂O, CL-20/CO₂, CL-20/N₂O systems. These mechanisms revealed that CO₂, N₂O and NH₂OH molecules inhibit the early stages of the initial decomposition of CL-20 and play an important role for the decomposition subsequently.

Host–guest energetic materials: a promising strategy of incorporating small insensitive molecule into the lattice cavities of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane to enhance the safety on the premise of maintaining the excellent energy density

A novel HNIW-MA host–guest explosive was constructed by embedding the mall molecules into the lattice cavities of HNIW, and it enhances the safety on the premise of maintaining its energy density.