Work

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

Year: 2025

Type: article

Abstract: Trans-scale interphase engineering, inspired by biomimetic modulus gradient design, was successfully implemented between rigid HMX crystals and soft F2314 binder. We demonstrated that F2314 chain mobility near the HMX surfaces is constrained by deliberately constructed nanoscale island structures, which promote the formation of a crystalline/semi-crystalline F2314 layer at the interface. This intermediate interphase creates a gradual modulus transition from the rigid HMX core, through the ordered interphase layer, to the soft amorphous matrix, resulting in an expanded interfacial region with a continuous gradient in mechanical properties. The engineered interphase redirects crack propagation through the graded layer rather than along the weak interface between HMX and F2314, thereby enhancing stress dissipation. Overall, the trans -scale interfacial architecture facilitates efficient stress transfer by redistributing applied loads between the HMX and the F2314 matrix, which significantly improves the composite’s damage resistance and interfacial stability. • Bioinspired modulus gradient engineered at HMX/F2314 interphase without chemical modifiers. • Enables efficient stress transfer, enhancing damage resistance and interfacial stability. • Nanostructures on HMX surface constrain F2314 chain mobility topologically. • Fosters crystalline/semi-crystalline F2314 layer formation at the interphase. • Interphase thickness correlates with F2314 crystallinity. 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.

Source: Materials & Design

DOI: 10.1016/j.matdes.2025.114518