Theoretical Studies On The Structure,properties And Desolvation Of Two-component Energetic Composites

Co-crystallization technology and host-guest inclusion strategy are two very promising methods for developing advanced high-energy density materials.Molecular dynamics(MD)and density functional theory(DFT)methods were adopted in this dissertation.The effects of different solvents on the crystal morphology of explosive HMX(1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane)were systematically studied;the supramolecular synthons of RDX(1,3,5-trinitro-1,3,5-triazinane)and different solvents were explored and analyzed,and their possible molecular packing was predicted by Monte Carlo simulations;the crystal and molecular structure,intermolecular interactions,surface structure and properties of TNT/aniline cocrystal were discussed;the surface properties,thermal behavior,stability,and desolvation process of HMX/N,N-dimethyl-formamide(DMF)cocrystal were studied;the driving force for the formation of different CL-20(2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaaza-isowurtzitane)solvates and the electric field assistant desolvation process of CL-20/DMF were studied;the crystal structure,electronic structure,mechanical properties,detonation performance,and interaction between host and guest of different CL-20 host-guest complexes were comparatively studied to clarify the effects of insert molecules;.The main contents of the dissertation are as follows:1.Influence of different solvents on the crystal morphology of explosive HMXThe interface model of HMX/solvent was constructed.The crystal morphologies of HMX in acetone and DMSO/H₂O solvents were studied using modified attachment energy(MAE)model and occupancy model based on MD simulations.Compared with the modified attachment energy model,the predicted morphologies from the occupancy model are more consistent with the experimental results.Radial distribution function(RDF)analysis indicates that there are extensive weak hydrogen bonds,van der Waals interactions,and Coulomb interactions between HMX and solvent molecules,among which the hydrogen bonds dominate the interactions between the solute and solvent-surface.Moreover,there are strong hydrogen bonds between the solvent and HMX in the DMSO/H₂O,though the number is relatively lower,it may have a greater impact on the crystal morphology than its contribution in the binding energies.2.Application of molecular electrostatic potential surface to predict supramolecular synthon for RDX/solvent cocrystalThe molecular electrostatic potential surface was utilized to predict the supramolecular synthons of RDX and different solvents,whose structures were studied and analyzed by DFT.The results based on Bader's atoms in molecules(AIM)and independent gradient model(IGM)show that unconventional CH···O type hydrogen bonds are the main intermolecular interactions between RDX and solvents.The result from crystal packing indicates that similar?-RDX/solvent supramolecular complexes tend to have the same symmetry during the crystallization process.All the predicted cocrystals were expected to have lower impact sensitivity than RDX.3.Structure,interactions,and surface properties of TNT/aniline cocrystalThe DFT method was used to study the structure and intermolecular interactions of TNT/aniline cocrystal and the charge transfer in the aniline molecules was analyzed based on ADCH charge.The results by the RDG method and ESP penetration graph show that the interlayer?-?interactions are the main force in the cocrystal,which leads to the charge transferbetween the aniline and TNT molecules.According to the Bravais-Friedel-Donnay-Harker(BFDH)method and attachment energy(AE)models,the habit of the TNT/aniline cocrystal in vacuum was predicted,and the surface properties of different crystal planes were explored by DFT and MD.According to the surface energies and kinetic properties of different crystal planes,it may be inferred that the desolvation of the TNT/aniline cocrystal is most likely to occur on the(200)crystal plane.4.Surface property,thermal behaviors,stability,and desolvation process of HMX/DMF cocrystalAccording to the crystal morphology of the HMX/DMF cocrystal,the slab model of its most important morphological surface was built to systematically study the thermal behavior and desolvation process via MD simulation.The internal energy,isometric heat capacity,mean square displacement,and diffusion coefficient were analyzed to estimate the structural changes and phase transition,and the melting point of the cocrystal is predicted to be 423K.The analysis of binding energy and RDFs suggests that the weakening of intermolecular interactions exist between HMX and DMF during the melting process.As the temperature rises,the trigger bond of HMX is elongated,leading to the decrease of its stability.5.Formation driving force and electric field assisted desolvation process of CL-20-based solvateThe crystal and molecular structures and intermolecular interactions of pure?-CL-20 and its solvates,namely CL-20/N,N-dimethylformamide(DMF),CL-20/1,4-dioxane(DO),and CL-20/N-methyl-2-pyrrolidone(NMP)were comparably studied by DFT and MD.The cocrystallization of CL-20 and different solvents will slightly affect the conformation of CL-20,which is mainly reflected in the bending of-NO₂ and the bond length of N-NO₂.Based on the Hirshfeld surface and RDFs,the hydrogen bonds formed between O_sol(from solvents)and H_CL-20(from CL-20)were found to be the driving force that promotes the formation of the cocrystals,while the O_CL-20-H_Sol interactions mainly contribute to the stabilization of the cocrystals.In the electric field strength range of 0.2-0.4 V?^-1,the DMF molecules in the CL-20/DMF cocrystal can diffuse in similar way as in the solution.The electric field assisted desolvation was observed as the solvent molecules in the CL-20/DMF move to the crystal surface along solvent channel and then reach the surface.6.Structure and properties of CL-20 host-guest compositesBased on DFT calculations,the effects of insert molecules were evaluated comparatively by studying the structural,electronic,energetic,mechanical and detonation properties of three host-guest crystals(CL-20/H₂O,CL-20/N₂O,and CL-20/CO₂)and anhydrous CL-20 crystals.The results show that the insertion of H₂O,N₂O,and CO₂ has few effects on the crystal and molecular structure of CL-20.But compared with pure CL-20 crystal,the small molecules enlarge the lattice cavities and density of states,and reduce the band gap of the host-guest crystals to some degrees.The analysis of the Hirshfeld surface and RDFs indicates that the inserted molecules interacted with CL-20 molecules through hydrogen bonds and van der Waals forces.The introduction of the three small molecules increases the bulk modulus and shear modulus of the CL-20 crystals,which indicates that the insertion of the guest molecules is helpful for increasing the stiffness and fracture strength of CL-20 crystals,among which CO₂ is the most effective.The introduction of the guest molecule improves the detonation performance of CL-20 to different extent,among which N₂O is the most effective.