3D printed high–strength polyimide aerogel metamaterials for sound absorption and thermal insulation

The structural manufacturing of high–performance polyimide (PI) aerogels is challenging because of the insufficient mechanical strength and rheological properties of sol–gel ink, and PI aerogels have limited application. In this study, a PI aerogel–based Helmholtz resonator (PIHM) and its acoustic metamaterial were innovatively constructed using freeze casting–assisted extrusion printing process and building block–assembly strategy, featuring a micro–perforated panel (MPP) sound–absorbing structure. The PIHM with a density of 0.294 g·cm⁻³ achieved a compressive strength of 10.2 MPa because of its periodically distributed honeycomb topology. Moreover, the PIHM not only retained the lightweight and thermal insulation characteristics of aerogels but also exhibited excellent sound–absorption performance because of the dual dissipation of sound waves by the MPP structure and PI aerogel framework. By serially connecting PIHMs with different aerogel pore sizes and leveraging the distinct acoustic properties of the layered structure along with the significant increase in relative mass resistance and acoustic impedance, the acoustic metamaterial achieved absorption coefficient peaks of 0.82–0.91 at 622–726 Hz, considerably widening the bandwidth with an absorption coefficient greater than 0.8. Finally, the composite sound–absorbing panel fabricated from a PIHM combined with common building materials demonstrated strong practicability and versatility. This research has pioneered a viable method for manufacturing PI aerogels with functional structures through 3D printing, expanding their application in the field of sound absorption and thermal insulation, and paving the way for the study of aerogel metamaterials in construction.