High-strength and multifunctional honeycomb polyimide aerogel fabricated by a freeze casting-assisted extrusion printing and building block-assembly strategy for sound absorbing metamaterials

The key issue of extrusion-based 3D printing of polyimide (PI) aerogels is the regulation of the ink rheology. Herein, a novel freeze casting-assisted extrusion printing method is proposed for the fabrication of honeycomb PI aerogels. Owing to the grid-like honeycomb structure with a periodic topological distribution, the compressive modulus of the honeycomb PI aerogel reached 63.5 MP at a density of 0.195 g·cm–3. Furthermore, the properties of the PI aerogels were synchronously regulated, e.g. the density (0.099–0.195 g·cm–3), the thermal conductivity (0.0382–0.0787 W·m–1·K–1), and the compressive strength (3.15–6.35 MPa), by manipulating the ink viscosity and honeycomb porosity. On this basis, a building block-assembly strategy of the printed PI aerogels was developed by controlling the temperature field and the gel's self-healing behavior, and two types of PI aerogel metamaterials for acoustic absorption were fabricated. These metamaterials exhibited enhanced overall sound absorption performance, with a new absorption peak with a sound absorption coefficient of 0.86 at a lower frequency. The freeze casting-assisted extrusion printing method can be extended to all solidifiable sol inks, and the building block-assembly strategy is inspiring for the general 3D printing of multifunctional aerogel materials and acoustic metamaterials.