The Research On The Influence Of Solvent Polarity To Explosive Cocrystal

In the energetic material fields,cocrystal explosive has been paid more and more attention by researchers as a new method of modifying the explosive.CL-20 is the most powerful single explosive which has been used at present.However,its sensitivity is high,which limits its application.The combination of CL-20 and other insensitive explosives to form cocrystal explosive can effectively improve its safety,and it is of great significance to heavily use it.In this paper,the effect of solvent polarity and molar ratio on the formation and morphology of CL-20/TNT and CL-20/MDNI cocrystal explosives are studied by quantum chemical density functional theory（DFT）and molecular dynamics（MD）method.These studies will provide the new method and idea for the design,preparation,control of morphology of insensitivy high energy cocrystal explosives.Follows are the main works in this paper:（1）A CL-20/TNT cocrystal-solvent interfacial model was established for the first time to study the effect of solvent polarity on the formation and morphology of cocrystal.Six kinds of solvents,namely,n-heptane,toluene,ethanol,acetonitrile,methanol and dimethyl sulfoxide,were selected.The morphology of CL-20/TNT cocrystal in the vacuum was controlled by four main growth surfaces:（002）,（111）,（020）and（021）.The molecular surface electrostatic potential shows that the surfaces of CL-20/TNT cocrystal can be divided into polar surfaces.The properties of solvent（such as polarity,dielectric constant,relative molecular mass,etc.）have an important influence on the formation and morphology of CL-20/TNT cocrystal.The binding energy and interaction energy show that CL-20/TNT cocrystsl is more easily formed in medium polar solvents（ethanol and acetonitrile）.The morphology of the simulated CL-20/TNT cocrystal in the ethanol solvent was basically the same as that obtained by the experiment.This proves that the method is correct and feasible.In addition,cocrystallization of solvents is a complex process,and the solvent can not only inhibit the crystal growth of specific surface,but also promote its growth.RDF analysis shows that there are intermolecular interactions between the cocrystal surface and the solvent layer.（2）The influence of different molar ratios of cocrystal component on the formation of CL-20/MDNI cocrystal was studied by MD method.The properties of cocrystal explosives at various molar ratios were calculated,including binding energy,the radial distribution function（RDF）,mechanical properties,trigger bond length and bond dissociation energy.The results show that the CL-20/MDNI cocrystal in molar ratio of 3:2 and 1:1 are more easily formed,and the detonation performance and stability are better;In the molar ratio of 3:2,elasticity and ductility of cocrystal are increased significantly;Due to the hydrogen bonds between CL-20 and MDNI,the trigger bonds of X-NO2 are enhanced,the sensitivity of CL-20 is decreased.（3）The CL-20/MDNI cocrystal in the molar ratio of 1:1 belongs to monoclinic（P2₁/c space group）,a=16.00?,b=11.07?,c=11.07?,α=β=γ=90°,which had eight major faces in vacuum.The surface of（200）is the roughest.The molecular surface electrostatic potential shows that these surfaces can be divided into polar surfaces.The interaction energy shows that CL-20/MDNI cocrystal is easier to form in ethanol and acetonitrile,and the interactions between（111）,（11-1）and solvent molecules are stronger.The morphology of CL-20/MDNI calculated by the MAE model is better in ethanol solution,which is prismatic,and the aspect ratio is 2.75.RDF analysis shows that hydrogen bonds,vdW and electrostatic interactions exist between hydrogen atoms of CL-20/MDNI cocrystal surface and the oxygen atoms of the solvent molecules.There are only hydrogen bonds between the oxygen atoms of the cocrystal faces and the hydrogen atoms of the solvent molecules,and the hydrogen bonds of（110）and（200）surface are stronger than those of the other crystal faces.