Molecular Dynamics Simulation Study On The Structure And Properties Of Energetic Composites And PVDF Membranes

In this paper,molecular dynamics?MD?simulation was performed to simulate the structures and properties of CL-20/HMX cocrystal,RDX composites and PVDF membranes.CL-20/HMX cocrystal?10 0?and?0 1 0?crystalline surfaces have larger cohesive energy densities and the binding energies than those of the cocrystal?0 0 1?crystalline surface,which indicated that the interactions between HMX and CL-20 molecules for the first two is larger,and their compatibility is better,the two systems are more stable.As for the three polymer bonded explosives?PBXs?,which HTPB was on the cocrystal surfaces?1 0 0?;?0 1 0?and?0 0 1?.respectively,the calculated binding energies showed that the order of the binding energies per unit surface between the crystalline surface and HTPB is?0 1 0?>?1 0 0?>?0 0 1?.The pair correlation function revealed that the H � O and H � N hydrogen bonds exist on the interfaces between the crystalline surfaces and HTPB.Additionally,the calculated mechanical properties indicated that the stiffness of the co-crystal/HTPB PBX is weaker and its ductility is better than that of the co-crystal.With the MPCFF force field,the RDX based compositite materials were carried out by MD simulations at five different pressures.The results showed that the trigger bond length,cohesive energy density and mechanical properties are related with the pressure.With the increasing pressure,the decreasing average bond length Lave of the trigger bond can be related to the sensitivity,the cohesive energy densities can not be correlated with the sensitivity due to the fluctuation of their values,and the stiffness and ductility are all increased.Under the same pressures,the two types of RDX composities with the different lengths of alkane molecular chains showed the similar properties.The diffusions of water and amides?DMF?DMAc?NMP?small molecules in the PVDF membrane were studied by MD simulations.We found that the diffusion of the small molecules was correlated with PVDF chain motility and membrane free volume fraction,though analyzing the movement of the PVDF chain and the free volume fraction?FFV?in PVDF membrane on the diffusion of small molecules.The results of MD simulation showed that PVDF organic membranes by blending PES and CA have stronger stiffness and stability than pure PVDF membrane.The performance of PVDF membranes filled with the different diameters of the SiO₂ particles were simulated.The calculation results showed that with increasing SiO₂ particles sizes,the binding ability of SiO₂ particles with PVDF chains enhances,the tensile and shear moduli increase,bulk moduli and the length of elasticity decrease.The MD simulations for the water diffusion properties in PVDF membranes filled with SiO₂ inorganic particles,revealed that the PVDF chain's motion ability and water diffusion rate are increased with the increasing size of SiO₂ particles.