Hydrogen bonds determine the nonbonding adhesion at HMX-based PBX interface

Polymer bonded explosives (PBXs) are kind of composite materials consisting of multi-layers structures, where the interfacial interactions can significantly affect their structures, properties and performance. To investigate the determinant factors affecting the interfacial interactions, in this work, the adhesion works at different interfaces are studied by molecular dynamics simulations. A key observation is that the hydrogen bonds are found to be a decisive factor that directly affects the interfacial interactions. When the fluoropolymers change from F2321 to F2319, the adhesion works with the HMX and coupling agent layer present a monotonous decrease and increase, respectively, corresponding to the changes in the number of weak hydrogen bonds. Thus the hydrogen bonds can be utilized to benchmark the nonvalent interfacial interactions. Moreover, the coupling agent layer as an intermediary enhances the adsorption between the explosive crystal and the binder, whose thickness significantly impacts the interfacial interactions. Its interactions with the HMX and fluoropolymers both show a similar increase with respect to its thickness and then stabilize at the thickness above 2.5 nm, corresponding to a surface density of six KH550 chains per nm². This study provides a basic understanding of the nonbonding adhesion mechanisms in the PBXs and is helpful for the material selection and structure design.