Simulation for the migration of nitrate ester plasticizers in different liners contacting with propellant by molecular dynamics

The liquid components, such as plasticizer, in the charge of solid propellant can potentially migrate into the liner contacting with propellant gradually, causing negative effects on the energetic performance, mechanical properties, and combustion properties of the propellant, as well as its interfacial adhesion properties with the liner. The study and prediction of the migration of the liquid components by experimental means remain challenging. In the present work, nitroglycerin (NG) and 1,2,4-butanetriol trinitrate (BTTN) were used as the model plasticizers to explore the factors affecting the migration of plasticizers into three different liners including polyoxyethylene (PEG)/polyisocyanate (N-100), hydroxyl-terminated polybutadiene (HTPB)/isophorone diisocyanate (IPDI) and polydimethylsiloxane (PDMS)/tetraethoxysilane (TEOS) by molecular dynamics simulation. The cohesive energy densities (solubility parameter), surface tensions, interfacial tensions, contact angles and diffusion coefficients of the plasticizers and liners were determined. It was found that the cohesive energy densities (solubility parameter) and surface tensions of the liner prepolymer and nitrate esters were in the order of PDMS<HTPB<PEG and BTTN<NG, respectively. The interfacial tensions and contact angles between the components followed the order of PEG-NG<HTPB-NG<PDMS-NG and PEG-BTTN<HTPB-BTTN<PDMS-BTTN, respectively. The interfacial tensions and contact angles values of NG are larger than BTTN. The diffusion coefficients of the nitrate ester plasticizers in various liners were in the order of PEG/N-100-NG>HTPB/IPDI-NG>PDMS/TEOS-NG and PEG/N-100-BTTN>HTPB/IPDI-BTTN>PDMS/TEOS-BTTN. Comparing different plasticizers, the order of diffusion coefficient in all liners is NG>BTTN, indicating NG is much easier to migrate into liners than BTTN. These simulation results are consistent with the experimental migration trends of NG into the corresponding liners, indicating that the molecular dynamics simulation can be used to study and predict the migration of plasticizers in various liners accurately and conveniently.