Self-reactive, in-situ generated PUA aerogels: Synergistic low-frequency noise attenuation via metamaterial-like structures and dynamically variation of acoustic impedance

Effectively attenuating highly penetrative low-frequency noise (LFN, f  < 500 Hz) presents a significant challenge. Traditional acoustic insulation materials are circumscribed by the mass law, presenting an inherent conflict between lightweight design and acoustic insulation. Despite the promising potential of PUA aerogels in acoustic insulation, attributed to their lightweight and high damping properties, their low-density results in inadequate areal density. Consequently, it remains challenging to effectively suppress LFN through mass inertia alone. Moreover, lightweight design often reduces mechanical properties, creating a conflict between lightweight, high strength, and low-frequency acoustic insulation. Inspired by the periodic structures of metamaterials, this study fabricates a PUA aerogel with an ordered metamaterial-like structure (density: 0.126 g/cm 3 ). Through self-assembly induced by sodium dodecyl sulfate (SDS), an ordered porous cavity and fibrous topological skeleton were formed. This structure creates an efficient interfacial reflection network that provides dynamic acoustic impedance for LFN attenuation. The average STL is at least 42.6 dB in the 45–500 Hz range and 39.6 dB in the broader 45–6300 Hz range, 16.35 times higher than that of commercial melamine foam of the same 2 cm thickness. Its weight is just 1/770 that of lightweight concrete bricks with equivalent noise reduction performance, and its thickness is only 2/25 of theirs. At 145 °C, the aerogel maintains a temperature difference of approximately 105.05 °C between its surfaces. The compressive strength of the modified aerogels is 2.76 times that of unmodified PUA aerogels. The simple, cost-effective fabrication process and the lightweight, high-strength, and outstanding low-frequency acoustic insulation properties make metamaterial-like PUA aerogels promising for noise reduction in residential, transportation, and industrial applications.