Construction of a rigid–flexible OVS/PHFA interphase on Al–Li alloy fuels for coupled stabilization and efficient energy release

Al–Li alloy fuels are attractive high-energy additives for solid propellants because their micro-explosion behavior can mitigate the severe agglomeration commonly encountered in aluminum fuels. However, their practical application remains constrained by hydrolysis, poor compatibility with binder/plasticizer matrices, and incomplete suppression of condensed-phase agglomeration during combustion. Herein, we propose a spatially integrated rigid–flexible interphase engineering strategy to reconcile the stability–reactivity trade-off of Al–Li alloy particles. Through interfacial thiol–ene click coupling and UV-initiated HFA–OVS radical grafting, rigid siloxane scaffolds and fluorinated polymer segments were spatially integrated within the same nanoscale interphase. Compared with the Al–Li@OVS@PHFA, the spatially integrated Al–Li@(OVS/PHFA) interphase exhibits stronger Si/F spatial association, higher interfacial binding, and improved structural continuity. Consequently, Al–Li@(OVS/PHFA) reduces hydrolytic gas generation by 95.9%, decreases hygrothermal weight gain from 187.61% to 3.27% after 30 d, and retains 97.5% of its energetic value. In BTTN compatibility tests, gas generation decreases from 62.52 to 1.09 mL g⁻¹, corresponding to a 98.3% reduction. More importantly, this protective interphase remains combustion-accessible, shortening the ignition delay by 70.7%, reducing the combustion duration by 46.2%, and further decreasing the agglomerate D₅₀ from 294.92 to 95.29 μm compared with pristine Al–Li. In propellants, Al–Li@(OVS/PHFA) delivers an apparent linear burning rate of 1.477 mm s⁻¹ and a heat of explosion of 11,496.1 J g⁻¹, further increasing these values by 6.2% and 10.9% compared with the stepwise Al–Li@OVS@PHFA counterpart. This work demonstrates that nanoscale spatial organization of rigid and flexible interfacial components can transform a protective coating into a multifunctional interphase that integrates environmental shielding, formulation compatibility, and combustion-stage activation, providing an architecture-guided route toward high-performance reactive metal fuels.