Hierarchical pore structure in polymethylsilsesquioxane (PMSQ) aerogel/PI foam composites for synergistically enhanced thermal insulation and low-frequency sound absorption

Polyimide (PI) foam combines the advantages of both resin and porous material, but its thermal insulation and sound absorption capabilities at low- and medium-frequencies are limited. To address these limitations, composite materials with superior multifunctional performance were developed by in-situ filling a PI foam matrix with high-surface-area, low-thermal-conductivity polymethylsilsesquioxane (PMSQ) aerogels. These hierarchical composites exhibit significant potential for thermal insulation and noise reduction. In this study, PMSQ aerogel/PI foam composites with hierarchical pore structure were prepared by using methyl triethoxysilane (MTES) as the silicon source, deionized water as the solvent, and PI foam as the matrix through a two-step acid-base catalyzed process, vacuum impregnation, and CO 2 supercritical drying method. Thanks to the meso-macroporous structure, the composites demonstrated excellent thermal insulation (thermal conductivity as low as 22 mW/(m·K)) and sound absorption performance. Notably, the sound absorption band shifted to the low-frequency direction compared with pure PI foam, achieving a peak absorption coefficient of 0.86 at low- and medium-frequencies for 10 mm-thick samples, coupled with an average sound transmission loss of 12 dB. The sound absorption performance of composites was simulated and verified based on the Johnson-Champoux-Allard (JCA) model, and the numerical simulation results showed good agreement with the actual experimental results. This work provides useful guidance for the microstructural design of advanced materials with integrated thermal insulation and noise reduction functions. Graphical