Chemically Programmable Underwater Sound‐Absorbing Metamaterial via MXene Self‐Assembly

Research on underwater acoustic metamaterials is constrained by a “geometry‐determines‐performance” paradigm, resulting in narrow bandwidth and complex fabrication processes. Here we introduce a chemically programmable metamaterial that overcomes this limitation by shifting the control logic from geometric design to intrinsic material programmability. Through the directed self‐assembly of MXene (Ti 3 C 2 T x ) nanosheets with polyvinyl alcohol (PVA), we fabricated a core film with a nanoscale quasi‐periodic layered structure, which was subsequently laminated with styrene‐butadiene rubber (SBR). The film integrates stable chemical cross‐links and dynamic hydrogen bonds into an editable chemical‐physical multi‐level constraint system. This architecture enables multidimensional programming capabilities. Chemically, adjusting the crosslinker concentration acts as a “chemical scissor” that broadly and continuously tailors the local resonance bands and dynamic states of the material. This programming operates at a deep subwavelength thickness of merely 10 mm, achieving an average absorption coefficient of 0.90 across the 1000–4000 Hz frequency range. Physically, modulating the film thickness and layer count provides an additional control dimension. This physical tuning strategy enhances low‐frequency performance, elevating the absorption coefficient at 600 Hz to 0.70. This work establishes chemical programming as a paradigm for designing metamaterials, transcending the limitations of conventional geometric approaches.