Ambiently Dried Aerogel-Foam Composites with Gradient Pore Structure for Enhanced Sound Absorption.

Silica-based aerogels are widely regarded as promising sound-absorbing materials due to their low density and high specific surface area. However, their hard surface and small pores hinder sound wave penetration, resulting in a relatively poor sound absorption performance. To overcome this limitation, our study employs melamine foam (MF) as a scaffold to construct a gradient aerogel composite acoustic absorber. This innovative design significantly leads to a low average density (31.3-117.4 mg/cm) and large density gradient up to 13.7 mg/cm (approximately 2.7 times difference compared with the lowest density), and its sound absorption properties are greatly improved, achieving an average absorption coefficient of 87% over the entire frequency band and 95% above 2000 Hz for 30 mm samples. In addition, the best noise reduction coefficient can reach 0.59. For demonstration, simulations further reveal the role of the pore size in enhancing sound absorption. The large pores in the foam skeleton facilitate the coupling of sound waves into the structure, while the small pores in the aerogel effectively block sound wave transmission, providing additional pathways for acoustic energy dissipation. Moreover, the incorporation of aerogel significantly enhances the foam's mechanical properties. In terms of thermal insulation, the presence of aerogel markedly improves the foam's insulating performance. This gradient design not only expands the potential applications of aerogels in sound absorption and thermal insulation but also provides a novel approach for the development of advanced acoustic materials.