Fabrication of large-sized robust carbon aerogel composites via pre-shrinkage-induced interfacial engineering

Abstract We report a strategy for synthesizing crack-free carbon aerogel (CA) composites by rationally matching the carbonization shrinkage of viscose fiber felts (VFs) with that of a phenolic resin (PR) aerogel matrix. The VFs were pretreated at elevated temperatures to induce controlled pre-shrinkage, followed by an in situ sol-gel transition and ambient-pressure drying of the PR precursor to produce large monolithic organic aerogels. By selecting a pretreatment temperature of 265 °C, the fibers and the matrix showed nearly identical subsequent carbonization shrinkages (26.2% versus 25.0%). This matched shrinkage drastically reduced residual stress, yielding a defect content of only 2% and a continuous, gradient interface without cracks or voids. The optimal composite achieved specific compressive and flexural strengths of 106.9 and 29.1 MPa·g − 1 ·cm 3 , respectively, along with a fracture toughness of 0.54 MPa·m 1/2 , significantly outperforming composites with mismatched shrinkages. Compared with conventional non-pre-shrunk counterparts, this design achieves a 91% reduction in residual stress and a 94% decrease in structural defects, resulting in 3.0-fold and 2.5-fold improvements in specific compressive and flexural strengths, respectively, as well as a 2.3-fold increase in fracture toughness. The design principle was further exploited to tune the matrix microstructure and density, and the material retained its structural integrity and superior high-temperature mechanical properties even at 1800 °C. This work demonstrates that controlling the shrinkage compatibility between reinforcement and matrix provides a versatile route to high-performance, large-sized CA composites for demanding structural and thermal applications.