Quantum Chemical And Dissipative Particle Dynamics Studies Of TATB-Based PBX

1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is the famous insensitive high explosive, and its based polymer-bonded explosives (PBX) are widely used. But the bindings between TATB and its polymeric binders are weak, which deduces the interfacial "bebonding" Therefore, the combination properties of TATB-based PBX are influenced and the applications of TATB-based PBX are limited. The coupling technique is a valid method to restrain the interfacial "bebonding". However, the understandings of the coupling mechanism of the coupling agent are insufficient. The selecting of the coupling agents in experiments is mainly based on explorations, so the theoretical guidance is urgently needed. Based on above, the intermolecular interactions between the recognized perfect TATB's coupling agent-the hydrolysate of y-Aminopropyltriethoxysilane (KH550) and the components of the TATB-based PBX are investigated at the microscopic level using the density functional theory (DFT) method. According to the optimized geometries of the mixing systems, natural bond orbital analysis and the intermolecular interaction energies, the coupling mechanism of the silane coupling agent in TATB-based PBX is predicated. In order to prove above prediction and observe the behavior of the hydrolysate of KH550 in TATB-based PBX visually, the dissipative particle dynamics method was used to investigate the mesoscopic morphologies, the distribution of the particle numerical density and some macroscopic properties of the TATB-based PBX with the addition of the coupling agent or not at the mesoscopic level. The results not only show the bonding mechanism between TATB and fluoropolymer, but also the behaviors of the coupling agent in TATB-based PBX. In addition, there is a close relationship between the warp of the fluoropolymers to TATB and the extension of the fluoropolymer in the different solvents and at different concentrations. So the dissipative particle dynamics method was used to investigate the two important parameters which can illuminate the extension of fluoropolymers-root mean square end-to-end distance and radius of gyration. Therefore, in which solvent and at which concentrations, the fluoropolymer being of the excellent warp properties to TATB is predicted. Our achievements and conclusions are as follows:At DFT-B3LYP-6-31G level, the intermolecular interactions between silane coupling agent and TATB are investigated, the three fully optimized geometries of the mixture and the electronic structures are obtained. Based on the natural bond orbital analysis, the great intermolecular charge transfer between silane coupling agent and TATB is mainly caused by the interactions between the lone pair electrons of oxygen atom in nitro group of TATB and antibonding orbital between O and H in the hydroxyl group of silane coupling agent; a strong hydrogen bond between the O of TATB and the H of the hydroxyl group of silane coupling agent is found. In addition, the accurate intermolecular interaction energies are calculated with zero point energy correction and basis set superposition error correction. The largest corrected intermolecular interaction of the mixtures is -17.969kJ/mol.Likewise, the intermolecular interactions between silane coupling agent and polymeric binder are investigated at the B3LYP/6-31G level by means of the density functional theory. Four fully optimized geometries of the mixture are obtained. The accurate intermolecular interaction energies are calculated with zero point energy correction and basis set superposition error correction. The largest corrected intermolecular interaction of the mixture is 24.514kJ/mol, which is larger than that of the silane coupling agent and TATB. Atomic net charges and nature bond orbital analysis is performed. Charge transfer between two molecules is great. The hydrogen bonds are formed in H...O and F...H. Based on the the largest corrected intermolecular interaction and the hydrogen bonds, it is predicted that the silane coupling agent will be in the aggregation of the polymeric binder in the mixture of the polymeric binder, silane coupling agent and TATB, rather than playing a molecular brigde role between filler and binder.In order to prove the prediction of the coupling mechanism of the silane coupling agent in the TATB-based PBX, which is predicted by means of the quantum calculations, the mesoscopic structures of TATB-based PBXs and their time evolutions were investigated using the dissipative particle dynamics (DPD) method. The results indicate that most of the polymers are condensed to spheres and only several polymer chains extend into TATB, the polymers form reseau structure in TATB; TATB is fixed in the polymers, but can not be wrapped perfectly by the polymers. At the same time, with the increasing of the temperature and the content of the polychlorotrifluoroethylene (PCTFE) monomers in the polymer, more polymers are dispersed in TATB. When the temperature is up to 400K, the polymers form the alveolate structure, and wrap TATB perfectly. In order to investigate the coupling mechanism of the silane coupling agent in TATB-based PBX, the mesoscopic morphologies of TATB-based PBXs, the assembly of the fluoropolymers and the distributions of the particle'numerical density were studied using the dissipative particle dynamics method. The TATB-based PBXs without the addition of the silane coupling agent are made as the references, the improvement of the bindings between TATB and fluoropolymers are analyzed according to the binding mechanism between explosive and polymeric binders-adsorption theory, wetting theory and diffusion theory, therefore, the interaction mechanism between TATB and fluoropolymer as well as the coupling mechanism of the silane coupling agent are obtained. The simulation results show the silane coupling agent being of an extraordinary coupling mechanism. The silane coupling agents pull the TATB'unaffinity group-chlorotrifluoroethylene structural unit together assembling inside of the fluoropolymers ball, while push the TATB'affinity group-vinylidene fluoride structural unit outside of the fluoropolymer ball. Because of the assembling of the TATB' affinity groups at the interface, the bindings between TATB and fluoropolymers are enhanced.The extension of F2311 and F2314 in ethyl acetate and butyl acetate solvents at different concentrations was also studied using the dissipative particle dynamics. It provides the theoretical date for selecting which solvent and which concentration for fluoropolymers being of the excellent warp properties to TATB. The results show that ethyl acetate is the good solvent for F2311, when the concentrations are below 10%, F2311 is of the excellent wetting effect to TATB. Butyl acetate is the good solvent for F2314, when the concentration is at 6%, F2314 is of the excellent wetting effect to TATB.In summary, the advanced quantum chemistry calculation method was used to investigate the intermolecular interactions between the coupling agent and the components of TATB-based PBX, and the dissipative particle dynamics was used to investigate the mesoscopic morphologies and some macroscopic properties of the TATB-based PBX. Our studies have enriched the studies of the formulation designs of polymer-bonded explosive and the improvement of the combination properties of polymer-bonded explosive, which are belong to the newest achievements of the quantum explosive chemistry and the large scale composite explosive chemistry.