Molecular investigations on the adsorption and flow behavior of hydroxyl-terminated polybutadiene (HTPB) binders on Cu surfaces: The effects of surface nanostructure and perfluorosilylation

The flow behavior of highly viscous casting explosives in micro-channels and special shaped moulds are critical factors affecting the formations of solid propellants and explosives. In the present work, the spreading property and flow behavior of hydroxyl-terminated polybutadiene (HTPB) binders, a major component of casting explosives, on Cu surfaces with nanostructures and perfluorosilylation were investigated by classical molecular dynamics simulations. Our results suggest that the atomic steps, exposed on the pit-/terrace-structured Cu surfaces, seem able to restrict the spreading of HTPB molecules from crossing over the step edges. After surface perfluorosilylation, the adhesive strength between HTPB and Cu substrate has decreased by nearly two orders of magnitude, resulting a vigorous travel of single HTPB molecules. Moreover, the cohesive strength between two adjacent HTPB droplets (-343.2 kcal/mol) is found to be higher than the adhesive strength of HTPB droplets on the perfluorosilylated smooth Cu surface ( - 85.7 kcal/mol). Thus, HTPB droplets could spread slowly on the perfluorosilylated Cu surface with a semi-spherical shape, irrespective of the presence of surface diatomic terraces. The reduced adsorption strength could also result in a slower infiltration speed of HTPB into the perfluorosilylated grooves and an increased slip performance on the perfluorosilylated surfaces.