Anisotropic and high-strength SiO2/cellulose nanofiber composite aerogel with thermal superinsulation and superhydrophobicity

SiO2 aerogel is a promising lightweight and high-efficiency thermal insulation material for applications in construction, industrial, aerospace vehicles, etc., but weak mechanical properties limit its further development and application. In order to overcome this challenge, we combined the design concepts of elastic group's introduction and structural strengthening of cellulose nanofibers with a directed freezing process, and successfully realized an anisotropic and high-strength SiO2/cellulose nanofiber composite aerogel. Under the low density of 0.247 g/cm3, the maximum compression strength of the aerogel in the radial direction is as high as 18.08 MPa, corresponding to a high fracture strain of 75.67%, and it also exhibits an excellent fatigue resistance, with only a slight plastic deformation of 6.5% after 100 load-unload cycles at a high compression strain of 50%. In addition, the aerogel exhibits an ultra-low thermal conductivity (0.01714W/(m·K)) in the radial direction, and also has a superhydrophobicity (water contact angle 150.8°) and a long-term hydrophobic stability (saturated mass moisture absorption rate 0.44%). The combination of these properties makes it an ideal material for thermal superinsulation in environments where both integrated mechanical properties and hydrophobic properties are critical.