Tough yet lightweight and flexible thermal insulative composite delivered by tendon-inspired gradient unit construction

Lightweight ablative thermal insulation composites are attractive for thermal protection in extremely harsh environments. However, the flexibility called for in applications such as morphing aerocraft is yet to be satisfied, especially with toughness and ablative resistance. Herein, for the first time, a bio-inspired tendon-like buffer of silicone rubber was employed to gradiently connect the inorganic quartz fiber and organic phenolic resin aerogel in the composite to develop flexible and tough ablative thermal insulator. The composite exhibited reversible compressibility and bendability, wherein the stress was 1.46 MPa and 0.47 MPa at 60 % compressive strain and 9 % bending strain, respectively. Additionally, the tensile strength was up to 2.39 MPa. It was self-ceramifiable at high temperatures, resulting in the ablation rate as low as 0.002 mm/s, which is favorable for ablation resistance and thermal insulation. We investigated and illustrated the ceramizing mechanism in detail. The outstanding hydrophobicity with the water contact angle of 138.8° is profit to the safety and durability of thermal insulators. The multi-functional composite opens up a new path to develop deformable thermal-protection materials with flexibility, roughness, hydrophobicity, self-ceramization, and thermal insulation for flexible thermal protection in harsh environments.