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 (Ti₃C₂T_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.