Gradient Pore-Structured\nPolymeric Fibrous Aerogels\nfor Effective Low-Frequency Noise Absorption

Traffic and industry noise have been considered the most\ndisturbing\npollutants that induce severe health hazards to humans. Porous materials\nare commonly used for sound-mitigating applications; however, realizing\nhigh elasticity and sound-absorption ability at low frequencies has\nremained a great challenge. Herein, we report a strategy to create\ngradient-structured ultralight weight and elastic polymer-based fibrous\naerogels by layer-by-layer assembly of polymer micro- and nanofibers\nin different combinations, utilizing step-by-step directional freezing\nand freeze-drying methods. This approach allowed us to integrate poly(ethylene\nterephthalate) microfibers (MF) and polyvinylidene fluoride nanofibers\n(NF) in different combinations, and the combination with MF/(MF and\nNF blend) MNF/NF units shows the best noise reduction coefficient\nof 0.66. Compared to the individual aerogels of MF, MNF, and NF, the\ngradient-structured fibrous aerogels show a better sound-absorption\nability at low frequencies. The gradient-structured fibrous aerogels\nexhibit ultralightweight, elasticity, and good mechanical properties.\nThe successful fabrication of these fascinating structures may provide\ninnovative prospects for the utilization of used plastics for the\nproduction of low-frequency noise absorbers.