Nano‐Engineered Interphase via Sol–Gel Route Enhances Hygrothermal Resistance of Basalt Fiber/Epoxy Composites

The mechanical performance and durability of basalt fiber (BF) reinforced polymer composites are often compromised by poor interfacial adhesion and susceptibility to hygrothermal degradation, despite the unique sustainable features of BF. Herein, we report the fabrication of a nano‐architected, organic–inorganic hybrid interphase on the BF surface via a synergistic sol–gel process of γ‐aminopropyltriethoxysilane (APTES) and tetraethyl orthosilicate (TEOS). An optimized 1:1 precursor ratio yielded a dense coating of about 10 nm nanoparticles grafted on the fiber, which provided a combination of maximized reactive amine groups for covalent bonding with the epoxy matrix, enhanced surface roughness for mechanical interlocking, and a hydrophobic barrier that reduced moisture absorption and diffusivity. Consequently, AT11‐BF/epoxy composites exhibited a 28.3% increase in initial short‐beam shear strength over pristine BF composites. Notably, the modified composites exhibited excellent hygrothermal durability, retaining over 90% of their initial short‐beam shear strength after 30 days of aging in 70°C water. This research presents an interphase engineering strategy to produce durable, high‐performance polymer composites for demanding applications.