Molecular investigation of adsorption behaviors of hydroxyl-terminated polybutadiene (HTPB) binders onto copper surface: The effects of aluminum nanoparticles

The adherent behaviors of hydroxyl-terminated polybutadiene (HTPB), a typical high viscosity liquid widely used as a binder in rocket motor propellants, onto the copper (Cu) surfaces with/without the interference of Al nanoparticles were investigated by classical molecular dynamics (MD) simulations. The results indicate that HTPB molecules adsorbed directly onto Cu(001) surface exhibit the tendency to distribute parallel to the 〈110〉 crystal direction family as a result of tense atom arrangement along the close-packed crystal directions. The dynamic hydrogen-bonded network, formed by inter-/intra-molecular interactions among neighbouring hydroxyl groups, is also suggested to exert strong influence on the distribution of HTPB molecules. Moreover, Al nanoparticles have been proved to be readily enveloped by HTPB chains when placed close to the pure high viscosity liquid, which will in turn restrict the mobility of HTPB molecules, eventually resulting in the decrease of wettability of HTPB droplet on Cu surface. The flow slip behavior of HTPB liquid on Cu surface, regardless of the presence of Al nanoparticles, was tested and directly compared by confined shear simulations. The Al hemispheres, acting as convex obstacles on the flat surface, seem to be capable of suppressing the slippage of chain-like HTPB molecules, which will be easily entangled by local protrusions. Therefore, it can be inferred that the flow behavior and interfacial wettability of high viscosity liquid will be largely influenced by the discontinuous solid-phase particles dispersed in it.