Towards the low-sensitive and high-energetic co-crystal explosive CL-20/TNT: from intermolecular interactions to structures and properties

Abstract

Employing molecular dynamic (MD) simulations and solid-state density functional theory (DFT), we carried out thorough studies to understand the interaction-structure-property interrelationship of the co-crystal explosive 1 : 1 CL-20 : TNT. Our results revealed that the co-crystallization of CL-20 and TNT molecules enhances the intermolecular binding forces, where the main driving force for the formation of the co-crystal CL-20/TNT comes from HO and CO interactions, while OO contributes to the co-crystal stabilization. Furthermore, we also used the concept of atoms in molecule (AIM) and the reduced density gradient (RDG) to describe the spatial arrangements and interactions of co-crystal compositions, which showed that although the adjoining TNT molecules possess two symmetry groups and the adjoining CL-20 molecules possess the same symmetry group, their interactions are not identical. These spatial arrangements provide a good reference to the formation of other co-crystals. When the obtained structural and detonation properties of the three crystals were compared, it was observed that the CL-20/TNT co-crystal achieved the desirable properties of explosives, i.e., low-sensitivity and high-energy, possessing the advantages of both CL-20 and TNT explosives.

Intermolecular interactions, vibrational spectra, and detonation performance of CL‐20/TNT cocrystal

“…The simulated lattice parameters and densities of all the three crystals were consistent with the experimental determinations, with relative errors below 5.5%, as shown in Table 4. [20,53] Afterward, the supercell of the above crystals was performed using the NVT-MD simulations (constant volume, constant temperature, and constant number of atoms) each for 80 ps with a time step of 0.1 fs at 300 K for RDF simulation.…”

“…The relationships between intermolecular interactions and detonation performance are presented in Table 1. [20] According to the "principle of the smallest bond order" (PSBO), the smaller the trigger bond order is, the bigger the sensitivity of an explosive is. [21] In a general way, the stability of energetic compounds may be evaluated via the statistical distribution of bond length obtained through classical MD simulations.…”

Electrostatic Balance Parameter Mediated Energy Functions‐Toward the Stability and Performance of Explosives

“…Supramolecular explosive is highly organized aggregates of coordination saturated energetic molecules through noncovalent interaction [45] (hydrogen bonds, π‐π stacking, van der Waals forces, and halogen bonds, etc.). In recent years, related studies [46–50] have shown the importance of designing supramolecular explosives to balance the energy and stability of explosives. As a high‐energy and low‐sensitivity explosive, CL‐20 has a detonation velocity of 9400 m ⋅ s −1 and an impact sensitivity ( H 50 ) of 24 cm [43], while LLM‐105, as a representative insensitive explosive, has a detonation velocity of 7820 m ⋅ s −1 and an impact sensitivity of 117 cm [44].To coordinate the energy and sensitivity of the two explosives, 6 kinds of supramolecular explosives with CL‐20 and LLM‐105 as subject and object at a molar ratio of 1 : 1 were assembled.…”

Intermolecular Vibration Energy Transfer Process in Two CL-20-Based Cocrystals Theoretically Revealed by Two-Dimensional Infrared Spectra

“…Cocrystal TNT/CL-20 shows different orientations along with different crystallographic directions; that is, the nitro groups of TNT and the piperazine rings of CL-20 form a repeating zigzagging chain along the [010] direction, and the adjacent CL-20 or TNT molecules form the [001] direction layer structures. Furthermore, interactions occur between the CL-20 nitro groups and the electron-deficient rings of TNT along the [120] direction [ 13 , 21 ]. Therefore, the structure of TNT/CL-20 includes a CL-20 and 3 adjacent TNTs with a total of 99 atom coordinates, as shown in Figure 1 left and Table S1 (In Supplementary Materials) [ 16 , 21 ].…”

“…Hübner et al characterized a nanoscale HMX/CL-20 cocrystal prepared by spray flash evaporation through tip-enhanced Raman spectroscopy and proposed that the HMX surface finishing might contribute to the impact sensitivity of HMX/CL-20 [ 19 ]. The major part of the theoretical approaches consisted of classical molecular dynamic simulations of intermolecular interactions, vibrational spectra and detonation performance, where the atomic interactions were based on sophisticated force fields [ 20 , 21 , 22 , 23 , 24 ]. All these works demonstrated that energetic cocrystals created a distinct solid-state arrangement at the molecular level and the intermolecular non-covalent interactions were the main driving forces for the cocrystal formation [ 25 , 26 , 27 ].…”