Strong acoustic meta-aerogels enabled by nanoconfined directional freezing and in-situ polymerization

Achieving low-frequency and broadband sound absorption in mechanically robust, space-efficient structures remains a central challenge in acoustic materials design. Here we report a nanoconfined freezing-assisted in situ polymerization strategy that enables the construction of acoustic meta-aerogels with hierarchical nano-micro-macro architectures. Under nanoconfinement, calcium-aluminosilicate hydrate nanoparticles nucleate and assemble along aligned microchannels, where nanoporous calcium-aluminosilicate hydrate phases anchored to the channel walls induce adsorption-desorption hysteresis, thereby generating a resonant-cavity-like acoustic response that enhances low-frequency absorption. This multiscale configuration, featuring aligned microscopic channels reinforced by strongly bonded calcium-aluminosilicate hydrate nanoparticles, facilitates efficient load transfer and structural integrity while promoting interfacial energy dissipation. The resulting aerogels exhibit low density ( ~ 50 mg cm^-³), high compressive strength ( ~ 1.88 MPa), and high toughness ( ~ 959 kJ m^-³), together with pronounced low-frequency absorption and broadband performance, with a noise reduction coefficient of 0.85 and sound absorption coefficient of 1.00 at 550 Hz, outperforming existing materials of comparable thickness. More broadly, this work establishes a general nanoconfined design strategy for engineering hierarchical acoustic materials, bridging nanoscale interfacial processes with macroscopic functionality and offering a versatile platform for multifunctional porous materials design.