Molecular Dynamics Simulation Study On The Structure And Properties Of RDX And CL-20/TNT Cocrystal And Their Composites

In this paper, molecular dynamics (MD) simulation was performed to study the physicochemical structure and properties of RDX and CL-20/TNT cocrystal and their composite materials.The RDX based compositite materials (RDX, Al, oil, paraffin, IPN, AP) were investigated with classical molecular dynamics by NPT-MD simulations at five different temperatures, andt the MPCFF forcefield modified by our group is used. The relationship of RDX based compositites engineering modules, Cauchy pressure, Poisson’s ratio, cohesive energy density (CED) and the maximum initiator bond length (Lmax) with temperature were studied. With the temperature increasing, the RDX based composities mechanical properties are improved, while the sensitivity increases at the same time. As compared with different formulation RDX composities, the coposities with IPN have a better mechanical properties and safety performance than the composities with AP. By these MD simulations, the formulation design of RDX based composities were enriched, and we also provide theoretical guidance for its application.Full-atomistic molecular dynamics simulations using COMPASS forcefield were performed to study the adhesion properties of different polymers onto different surfaces of CL-20/TNT cocrystal. The polymers studied in this paper include polyvinylidene fluoride (PVDF), the copolymers of vinylidene fluoride (VDF) and chlorotrifluoroethylene (CTFE) F2311 and F2313, polyvinyl acetate (PVAc) and cis-polybutadiene rubber (BR). Comparing the results of the interfacial tension, work of adhesion and spreading coefficient with different polymers onto different cocrystal surfaces, all of the five polymer binders can spread onto cocrystal surfaces, and the F2313 polymer has the optimal spreading performance onto (010)T/H surface. Detailed analysis showed that the adhesive properties of the polymer binders and CL-20/TNT cocrystal are determined by the molecular structure of polymer and the surface structure of the cocrystal. These researches provide reference for the binder selection of CL-20/TNT cocrystal based PBXs.The semi-empirical quantum mechanics molecular dynamics (QMMD) which is based on self-consistent charge density-functional tight-binding (SCC-DFTB) theory was employed to study the CL-20/TNT cocrystal thermal initiator procedure. The canonical ensemble (NVT) MD simulations for CL-20/TNT cocrystal unitcell were carried out at a temperature of 2800K, and the cocrystal decomposition initial reaction, pyrolysis reaction path of CL-20 and TNT molecules and product distribution were analysised meticulously. Investigating the decomposition reaction by QMMD simulations reveals the CL-20/TNT cocrystal material thermal initiator mechanism, and will lay a foundication for researching the safety property of this cocrystal material.