Molecular Dynamics Simulation Study On The Structure And Properties Of CL-20/DNB Cocrystal Based PBX And PVDF/PES Membrane

In this dissertation, molecular dynamics (MD) simulation was conducted for CL-20/DNB cocrystal and their composite materials using COMPASS force field, as well as for membrane materials composited by polyvinylidene fluoride (PVDF) and polyethersulfone (PES).The CL-20/DNB supercell was built firstly, and then the supercell was cutted along crystal surfaces (001), (010) and (100) for building "cutting models". For more studies on crystal surface (001), four cutting models were built by cutting along four different positions.In the study, we found that two cutting models were lower than the supercell in density, cohesive energy density (CED) and binding energy, they are the cutting model along (100) crystal surface and the first cutting model along (001) crystal surface respectively. But the other cutting models are all similar to the supercell. The vdW interactions component is the leading cause for energy decreasing. The pair correlation function g(r) reveals that the hydrogen bond interactions mainly derive from H of CL-20 and O of DNB. Adding a small amount of polymer binder polyethylene glycol(PEG) to prepare CL-20/DNB cocrystal-based PBXs (polymer bonded explosives), and conducting molecular dynamic simulations (MD) for the PBXs. From the studies, we found that the binding energy between PEG and the third cutting model along (001) crystal surface is the biggest one, and g(r) reveals that there are more hydrogen bond between PEG and the third cutting model along (001) crystal surface. The mechanical properties of PBXs are improved after adding PEG. We calculated the diffusion coefficients of the explosive molecules contacted with PEG chain. By comparisons, it was found that the diffusion coefficient of the explosive molecules in (001)/PEG is the smallest one, and it tells us that the interfacial explosive molecules in (001)/PEG are prevented from migrating away by PEG chain. Furthermore, the hindering effection in the system is the strongest, and it corresponds to the binding energy too.In the three oil systems, the order of diffusion coefficientsfor water molecules is n-Hexadecane> paraffinic oil> naphthenic oil. The major interaction between water molecules and oil molecules is vdW interactions, and the electrostatic interaction is so week that we can ignore its contribution to the interactions between oil and water. This reflects the nonpolar characters of oil molecules. Adding Polyethersulfone (PES) into polyvinylidene fluoride (PVDF) by the ratio of 5:5, then we studied the oil-water separating property of the blending polymer membrane. Found that the hydrophility of the membrane become better, and the mechanical properties are also improved to bear higher transmembrane pressure. But the diffusion coefficients of water molecules in PVDF/PES blending polymer membrane were lower than these in PVDF membrane.In the aspect of oil-water separating property, the the diffusion coefficients of water molecules in blending polymer membrane are all lower than PVDF membrane. This phenomenon indicates that the free volum in the membrane materials has been decreased, and there are fewer chances to didperse away for water molecules. Therefore, we should continue to do more modifications for PVDF/PES blending polymer membrane. When we start to do the further modifications, we must consider whether the modification can make the free volume bigger in the membrane materials.