Molecular Mechanism Of MeNQ-based Eutectic Formation

TNT is the most commonly used liquid phase carrier of molten cast explosives in the fields of industrial demolition and weapons and ammunition,but TNT has a number of drawbacks,including high thermal sensitivity,a serious tendency to subcooling,toxicity,and so on.As a result,during the molding,storage and use processes,molten cast explosives taking TNT as liquid phase carrier exhibit oil seepage,brittle,hollow,and poor environmental adaptability etc.,and its energy level can not meet the current requirements of weapons and equipment for efficient destruction.It is an important research direction in the field of energetic materials to replace TNT with new energetic eutectic to obtain pollution-free and high-performance molten carrier explosives which meet the standard of insensitive ammunition.Since the beginning of the 20th century,a large number of energetic eutectic systems have been reported at home and abroad.The current research methods for energetic eutectic are mainly based on experiments,focusing on formulation and performance testing as carrier explosives.However,the formation mechanism at the atomic and molecular level of energetic eutectic is still unclear,which seriously restricts the development of energetic eutectic.Based on this,this paper investigates the molecular mechanism of the formation of MeNQ-based energetic eutectic using MeNQ/NQ and MeNQ/HN binary eutectic system as the object of study and MeNQ/AN binary cocrystal system as the comparison sample,and employs various simulation methods to investigate the molecular mechanism of the formation of MeNQ-based energetic eutectic based on intermolecular interactions.The main studies are as follows:（1）Study of intermolecular interactions in dimers:Based on the basic principles of hydrogen bond formation,all possible homodimer and heterodimer models of three binary systems,MeNQ/NQ,MeNQ/HN and MeNQ/AN,were constructed and structurally optimized using the M06-2X-D3/6-311+G（d,p）method to obtain the lowest energy structures.The intermolecular interaction energies of the dimers were calculated using high-precision first-principles methods（MP2/may-cc-pvtz and PWPB95-D3/ma-def2-QZVPP）,and the relative errors of the results calculated using two methods did not exceed 3%,and the intermolecular interaction energies of the homodimers in all three binary systems were larger than those of the heterodimers.The most stable dimer structure is selected for energy decomposition analysis.The results show that electrostatic attraction is the main source of intermolecular interaction energy.The location,intensity and type of molecular interactions between dimers were studied by electron density topology analysis and reduced density gradient function analysis.（2）Flory-Huggins interaction parameters(c_AB)study in binary system:The dimer model only considers the interaction between two molecules,which is a description of a specific"point"of intermolecular interaction and does not fully reflect the intermolecular interaction in the whole system.Based on this,this chapter calculates the mixing energy and c_AB of three binary systems,MeNQ/NQ,MeNQ/HN and MeNQ/AN,based on the intended Flory Huggins theory model,using the Monte Carlo simulation combining with molecular mechanics method,the mixing energy and c_ABof MeNQ/NQ,MeNQ/HN and MeNQ/AN three binary systems are calculated.Results show that the simulated temperature range of 100～800 K,the mixing energy and c_ABof MeNQ/NQ and MeNQ/HN binary systems are positive,and with the increase of temperature gradually close to zero,explanning the cohesive interaction（the interaction between same molecule）of the two systems is greater than the adhesive interaction（the interaction between different molecule）.By contrast,the mixing energy and c_ABof MeNQ/AN binary cocrystal system is always negative,shows that the strong adhesive interaction in the system.（3）Interaction energy study in binary system:c_AB is calculated with high efficiency but low accuracy.In order to further verify the relative balance of molecular interactions in eutectic systems,theoretical models of three binary systems:MeNQ/NQ,MeNQ/HN and MeNQ/AN were constructed in this chapter,and the interaction energy is calculated using the first-principles method with higher accuracy.The results show that the interaction energies of MeNQ/NQ and MeNQ/HN are both positive,indicating that cohesive interaction is dominant in the system.The interaction energy of MeNQ/AN binary system is negative,indicating that the adhesive interaction is dominant in the system.The calculation results of the first principles are consistent with the Monte Carlo simulation combining with the molecular mechanics method.All the simulations illustrate that for the binary eutectic systems of MeNQ/NQ and MeNQ/HN,the cohesive interaction is stronger than the adhesive interaction in the system,and both the c_AB and interaction energy are positive,while in the MeNQ/AN binary cocrystal system,it is just the opposite.Considering the computational efficiency,c_AB>0 can be used tentatively as an energy criterion for the formation of eutectics.