Investigations On The Effect Of Component Ratio And Solvent Behavior On The Crystallization Of Explosives

1,3,5,7-tetranitro-1,3,5,7-tetrazacyclo octane(HMX)and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexazisowurtzitane(CL-20)are two kinds of high energy single explosives,but the high sensitivity has limited their application.Therefore,it is of practical significance to improve their safety.Based on the supramolecular principle,the HMX/1-methyl-4,5-dinitroimidazole(MDNI)cocrystal model was built,and interfacial models of isopropanol(IPA)-CL-20/HMX and solvent-CL-20 were also established.Density functional theory(DFT)and molecular dynamics(MD)methods were employed on the two kinds of models mentioned above to analyze and be verified by experimental result.Results of this paper can provide some experience and guidance for the improvement of explosive safety and understanding of the solvent effect on the explosive performance.The specific research work is as follows:(1)Different molar ratios of HMX/MDNI cocrystal and complex models were designed.The binding energy,radial distribution function(RDF)and mechanical properties of the HMX/MDNI cocrystal model at all molar ratios were studied,and the complex structures,bond dissociation energy(BDE)of trigger bond as well as electrostatic surface potential(ESP)were analyzed.The prediction results show that the binding energy and intermolecular interaction are the largest at the molar ratio of 1:1(HMX:MDNI),meanwhile the comprehensive mechanical properties are better.The formation of HMX/MDNI cocrystal explosive is mainly based on the C�O���H hydrogen bond interaction.Moreover,weak C/O���O dispersion interaction can also be found.BDE and ESP results show that BDE of HMX trigger bond is increasing and the sensitivity is decreasing,thus enhancing the safety of HMX,because of the intervention of MDNI.(2)The effect of solvent behavior at different temperatures on the cocrystal surface growth has been studied for the first time.IPA-CL-20/HMX interfacial models at different were established.The solvent mass distribution function,diffusion capacity,average adsorption energy,radial distribution function and the relative changes of modified attachment energy under different temperatures were analyzed from the differences of solvent behavior.Results showed solvent density at(1 0 0)and(1 1 1)faces is larger and the interaction is stronger.The diffusion capacity of solvent at higher temperature(355 K)is more than 2 times higher than that of lower temperature(295 K).It?s easier to form O���H hydrogen bond with solute molecules at 295 K,indicating that interaction of the solvent at low temperature is stronger and the solvent molecules play a more vital role on the cocrystal growth.Polarities of(1 0 0)and(0 1 1)cocrystal surfaces,predicted by DFT method,are more negative and easily affected by IPA.The predicted cocrystal morphology(295 K)by simulation is consistent with the experimental result.(3)The effect of interaction between solvent and surfaces on the crystal growth has been investigated from the different roughness of CL-20 surfaces for the first time.The interfacial models of CL-20 with methanol(ME),ethanol(ET),ethyl acetate(EA)and acetone(AC)were constructed,respectively.The DFT with dispersion correction was used to analyze the ESP of CL-20.The four solvent-CL-20 interfacial models were simulated by MD simulation.The results show that differences of ESP at the main growth surfaces are caused by the exposed functional groups and the roughness of cocrystal surfaces,therefore the interaction with solvent and the surface growth will be influenced.RDF analysis shows that the percentage of C�H���O distance(less than 3.1 ?)is up to 60%,indicating that there are strong intermolecular hydrogen bond at each interfacial models.Interaction at the rougher face is stronger than that of smoother surface.The equilibrium trajectory shows that the solvent molecules will "reside" at the recess of rough crystal surface,so the inhibition effect on the growth of rough cocrystal surface is more obvious,while the effect on the smooth surfaces is slight.