Programmable Gradient-Pore Architectures in Hybrid Aerogels via Layer-by-Layer Directional Freezing for Enhanced Broadband Acoustic Absorption Performance.

Prolonged noise exposure poses significant health hazards to humans; however, conventional sound-absorbing materials, predominantly single-structured, exhibit inadequate performance in attenuating noise across broadband frequency ranges. To address this limitation, a programmable three-layer gradient-pore structured aerogel incorporating a tri-component fiber hybrid (cellulose nanofibers, aramid nanofibers, and quartz fibers) was constructed via layer-by-layer directional freezing. The gradient-pore architecture enables multilayer collaborative "frequency-band-partitioned impedance-matching" optimization: the outermost large-pore layer reduces direct sound reflection, efficiently absorbing more acoustic waves (especially for high-frequency ones) into the aerogel; the innermost small-pore layer reflects more waves (especially for high-frequency ones) backwards rather than permitting transmission; and the mid-pore interlayer acts as a transitional zone, enhancing multireflection and scattering-induced energy dissipation. Consequently, this gradient-structured aerogel demonstrates superior broadband sound absorption capacity compared to its single-structured counterparts. Additionally, it exhibits exceptional mechanical robustness, stability across a broad temperature range, and notable water repellency following hydrophobic modification. This work provides critical insights for developing gradient-structured aerogels with broadband acoustic absorption properties, thereby advancing their application potential in related fields.