Trans-scale interphase engineering for enhanced interfacial reinforcement between ‘rigid’ HMX crystals and ‘soft’ binders

Polymer-bonded explosives (PBXs) balance energy density and mechanical performance by integrating rigid high-energy crystals within soft polymer matrices. However, interfacial incompatibility from large modulus mismatch induces inefficient stress transfer, localized stress concentrations, and premature failure. Inspired by biological modulus gradients bridging soft/hard tissues, we engineer the octahydro-1,3,4,7-tetranitro-1,3,5,7-tetrazocine (HMX) / F2314 interface via in situ construction of nanoscale surface structures dimension-matched to the radius of gyration (R_g) of F2314 chains. These nanostructures act as molecular anchors, constraining polymer mobility to induce a crystalline/semi-crystalline interphase. This yields a sixfold-thicker interphase (509 ± 42 nm vs. 67 ± 25 nm), establishing a continuous mechanical gradient from rigid HMX to soft matrix. The gradient interphase shifts failure modes from interfacial debonding to cohesive matrix rupture and trans-granular fracture, confirming enhanced stress transfer. Mechanical/morphological analyses verify improved load-bearing without compromising energetic performance. Crucially, this modifier-free strategy enables scalable interfacial reinforcement for next-generation PBXs. Crack redirection through the graded interphase and optimized stress distribution significantly enhance damage resistance and interfacial stability.