Research On Design And Controlled Assembly Of Nitroamine Explosive Cocrystal

Now,cocrystal energetic material has become an effevtive way to modify high-energetic explosives.The adjustment of the physical and chemical properties of the cocrystal energetic material can be realized through the slight changes of arrangement mode and stacking mode in supramolecules.2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane?CL-20?and1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane?HMX?are two kinds of nitroamine explosives with excellent properites in active service.The theory detonation velocity of CL-20 and HMX exceeds 9000 m/s.However,high sensitivity of CL-20 and HMX limits their application in mixed explosives and propellants.To improve the safety performance of CL-20 and HMX,five cocrystals were preparaed via solvent evaporation method and green ball milling method.Meanwhile,the influence of cocrystal strategy on the property of energetic materilas,the characteristic of intermolecular interactions in cocrystal structure,and the assembly mechanism of cocrystal supermolecule were investigated.The main researches are as follows:?1?Hirshfeld surface,the corresponding 2D fingerprint plots,the color-filled reduced density gradient?RDG?maps,the color-filled noncovalent interactions?NCI?plots and molecular electrostatic potential surfaces?ESP?were analysized to quantify the type,position,intensity,frequency and charge density distribution of intramolecular and intermolecular interactions in CL-20,HMX and TNT at the molecular level,speculate the molecular reactivity site and predicte the self-assembly type of cocrystal supermolecule by computational quantum chemistry.The results show that the strongly negative ESPs with strong electron-withdrawing ability concentrates on the nitro groups in CL-20,HMX,and TNT.Moreover,a large number of strong hydrogen bonds and van der Waals forces,the main driving forces for cocrystal,stimulates the formation of cocrystal.?2?CL-20/TNT cocrystal?crystal 1?was preparaed via green solvent evaporation method and micro/nano CL-20/TNT cocrystal?crystal 2?was preparaed via green ball milling method.The samples were characterized by single-crystal X-ray diffraction?SXRD?,powder X-ray diffraction?PXRD?,scanning electron microscopy?SEM?,fourier transform infrared spectroscopy?FT-IR?,Raman spectroscopy?Raman?,X-ray photoelectron spectroscopy?XPS?,differential scanning calorimetry?DSC?.Furthermore,the explosive performance and safety performance of samples were also analysized.The results show that in SXRD,the building units of crystal 1 are CL-20 and TNT molecules with molar ratio 1:1 and the crystal density is1.934 g·cm^-3,which confirms that the crystal 1 is CL-20/TNT cocrystal with high density.The results of PXRD,FT-IR and Raman confirm that the crystal 2 is micro/nano CL-20/TNT cocrystal.In SEM,the morphology of crystal 1 is hexahedron with 1 mm.The crystal 2 is irregular spherical with 80 nm⁶00 nm.In XPS,the chemical elements of crystal 1 didn't change before and after cocrystal.In DSC,the thermal stability of crystal 1 and crystal 2 is improved.The detonation velocity of crystal 2 is 8631 m·s^-1 and both crystal 1 and crystal 2show a better safety performance than CL-20.In Hirshfeld surface analysis,a large number of strong intermolecular interactions exist in cocrystal structure.In 2D fingerprint plot,more kinds of intermolecular interactions indicate that CL-20/TNT cocrystal has a better safety performance than CL-20.In RDG analysis,there are obvious hydrogen bonds and van der Waals forces in CL-20/TNT cocrystal.In ESP analysis,the detonation velocity of raw and cocrystal decreases in the order of CL-20>CL-20/TNT>TNT,while the impact sensitivity of raw and cocrystal decreases in the order of CL-20>CL-20/TNT>TNT,according to the maximum of ESP.Eventually,the structure model of the heterogeneous nucleation in crystal 1and the mechanism model for crystal 2 self-assembly processes were proposed in this dissertation.?3?CL-20/HMX cocrystal?crystal 3?was preparaed via solvent evaporation method and micro/nano CL-20/HMX cocrystal?crystal 4?was preparaed via green ball milling method.The samples were characterized by SXRD,PXRD,SEM,FT-IR,Raman,XPS,DSC,detonation velocity and mechanical sensitivity tests.The results show that in SXRD,the building units of crystal 3 include CL-20 and HMX molecules with molar ratio 2:1,which confirms that the crystal 3 is CL-20/HMX cocrystal.The results of PXRD,FT-IR and Raman confirm that the crystal 4 is micro/nano CL-20/HMX cocrystal.In SEM,the morphology of crystal 3 is polyhedron with 350?m.The crystal 4 is irregular spherical with with 50 nm²00 nm.In XPS,the chemical elements of crystal 3 didn't change before and after cocrystal and and the samples are very pure.In DSC,the thermal stability of crystal 3 and crystal 4 is improved.The detonation velocity of crystal 4 is 8724 m·s^-1 and both crystal 3 and crystal 4 show a better safety performance than raw materials.In Hirshfeld surface analysis,weaker intermolecular interactions make CL-20/HMX a better safety performance.In 2D fingerprint plot,more kinds of intermolecular interactions further indicate that CL-20/HMX cocrystal has a better safety performance than raw materials.In RDG analysis,there are obvious hydrogen bonds and van der Waals forces in CL-20/HMX cocrystal.In ESP analysis,according to the sum of maximum and minimum of ESP,the detonation velocity of raw and cocrystal decreases in the order of CL-20>HMX>CL-20/HMX,while the impact sensitivity of raw and cocrystal decreases in the order of CL-20>HMX>CL-20/HMX,according to the maximum of ESP.Eventually,self-assembly mechanism of crystal 3 and crystal 4 were proposed in this dissertation.?4?Micro/nano HMX/TNT cocrystal?crystal 5?was preparaed via green ball milling method.The raw materials and cocrystal were characterized by SEM,PXRD,FT-IR,Raman,XPS,DSC,detonation velocity and mechanical sensitivity tests.The results show that the morphology of crystal 5 is irregular spherical with 50 nm³00 nm.The results of PXRD confirms that the crystal 5 is micro/nano HMX/TNT cocrystal.In FT-IR and Raman analysis,there are shift,addition and disappear in spectral peaks of cocrystal 5.In XPS,the samples are very pure.In DSC,the thermal stability of crystal 5 is improved.The detonation velocity of crystal 5 is 7300 m·s^-1 and the crystal 5 shows a better safety performance than raw materials and simple mixtures.Eventually,self-assembly mechanism of crystal 5 was proposed.