Density functional theory study on the interaction mechanism between a neutral polymeric bonding agent and cyclotetramethylene tetranitramine (β-HMX) surfaces

Neutral polymeric bonding agents (NPBAs) improve the mechanical properties of nitrate ester plasticized polyether (NEPE) propellants by enhancing the interfacial adhesion between cyclotetramethylene tetranitramine (β-HMX) particles and the binder matrix. To elucidate the interaction mechanism between NPBA and HMX surfaces, this study performed a detailed investigation using density functional theory calculations, focusing on adsorption energy, the Independent Gradient Model based on Hirshfeld partition (IGMH), molecular electrostatic potential, energy decomposition analysis (EDA), and electron density difference. The results indicate that the crystal face is the primary factor influencing binding strength, due to differences in the arrangement of HMX molecules on the surface. The binding strength of NPBA is strongest on the (010) face of HMX, followed by the (011) and then the (110) face. Furthermore, both the adsorption conformation and the orientation of functional groups in NPBA affect the binding strength. The former strengthens binding mainly by increasing the contact area with the HMX surface in a spreading manner, whereas the latter enhances adhesion through the formation of hydrogen bonds (O - H···O and C - H···O) with HMX molecules. The interaction between NPBA and HMX is physical adsorption, co-dominated by electrostatic and dispersion interactions.