Constructing a multiscale rigid-flexible interfacial structure at the interphase by hydrogen bonding to improve the interfacial performance of high modulus carbon fiber reinforced polymer composites

Carbon fiber reinforced polymer composites (CFRPs) have many irreplaceable advantages not found in metals or ceramics, such as high specific modulus, superior tensile strength, and ultra-lightweight. However, their limited interfacial properties and the expanded modulus difference between carbon fibers (CFs) and host matrices still prevent effective transmission of stress and cause stress concentration at the interphase and deteriorate the mechanical properties of CFRPs. Therefore, we presented to construct a multiscale rigid-flexible interfacial structure at the interphase to balance the modulus of fibers-matrix and improve the surface wettability of high modulus CFs to improve interfacial properties of CFRPs. The multiscale interface is multistage gradient interlayers constructed by strong physicochemical interactions with a thickness of ∼463 nm. The structure consists of flexible water-soluble epoxy (WEP) and rigid graphene oxide (GO) through hydrogen bonding. The resultant CFs integrate rough surface (Ra = 57.20 nm), numerous oxygen-containing functional groups (O atomic% = 21.44%), huge BET surface area (1.250 m2/g), and superior monofilament tensile strength (5.204 GPa), which allows CFPRs to achieve strong interfacial bonding. The modified CFRPs with rigid-flexible interfacial structure show robust interfacial properties, the value of ILSS and IFSS respectively increased by 25% and 55% over the untreated counterparts, which enables effective stress transfer between CFs and host matrices. This strategy of combining rigidity and flexibility opens an avenue toward the development of materials with superior interfacial performance for various inert high modulus fibers.