Robust, thermally insulating and hydrophobic resorcinol–formaldehyde modified SiO2 aerogels with interpenetrating network structure

The inherent brittleness of pure SiO 2 aerogels due to the fragile Si–O–Si bonding connection at the neck greatly limits their applications. The limitations in mechanical properties of SiO 2 aerogels can be effectively overcome through the recent advancements in organic–inorganic hybrid systems. In this paper, resorcinol- formaldehyde (RF) reinforced silica aerogels (RSA) were synthesized using tetraethyl orthosilicate (TEOS) as the silicon precursor through a two-step sol–gel approach coupled with an ethanol supercritical drying process. The structural evolution and properties of aerogels during RSA's preparation were studied in relation to RF sol properties, gelation catalysts, and the doping content of RF sol. In particular, the aerogels crosslinked with γ-aminopropyltriethoxysilane (APTES), exhibit multifunctional properties including a high specific surface area of 802 m 2 /g, a low density of 0.208 g/cm 3 , a low thermal conductivity of 0.0230 W/(m·K), good hydrophobicity (a water contact angle of 141.5°) and compressive strength (0.58 MPa at 10% strain). The thermally insulating, hydrophobic and robust resorcinol–formaldehyde modified silica aerogel materials have positive significance in expanding the applications of silica aerogels.