Frequency-selective sound absorption in transparent polymer composites with monodisperse hollow silica spheres

Hollow silica spheres possess unique properties such as high surface area, low refractive index, and light weight because of their hollow cores. These traits make them ideal for various applications, particularly as sound absorption materials. In this study, hollow silica spheres and their polymer composites, which exhibit frequency-selective sound absorption properties, were developed. Hollow silica spheres were prepared using polymer core templates, followed by calcination, resulting in highly monodisperse spheres with a uniform size distribution. By incorporating these spheres into a polydimethylsiloxane (PDMS) matrix, we demonstrated that sound absorption peaks can be tuned by adjusting the filler content, allowing frequency-selective absorption—in sharp contrast to typical broadband-absorbing porous materials. Notably, the inclusion of hollow silica spheres significantly enhanced the optical transparency of the composite by reducing the refractive index mismatch at the interfaces. Our findings highlight the potential of transparent, monodisperse hollow silica sphere-based isotropic composites with precisely controlled acoustic responses as versatile materials for next-generation acoustic and optical applications.