Enhanced interfacial adhesion of carbon fiber/epoxy composites by synergistic reinforcement with multiscale “rigid-flexible” structure at interphase

Carbon fiber (CF) reinforced matrix composites have wide application prospect, however, the interfacial adhesion of composites is weak due to smooth and chemically inert of CF surface. To settle this problem, two kinds of synergistic hierarchical reinforcements with multiscale “rigid-flexible” structures [CF-graphene oxide (GO)-carbon nanotubes (CNTs)- polyamide (PA) and CF-CNTs-GO-PA] were fabricated through simple esterification and anionic polymerization reactions. The effects of the interface thickness and grafting sequence on the interfacial properties of the composites were explored. The interfacial shear strength (IFSS) of the CF-GO-CNTs-PA/resin composites was 88.3 MPa, which exceeded those of CF, CF-GO-CNTs, CF-GO-PA, and CF-CNTs-GO-PA by 80.9%, 11.5%, 2.3%, and 1.4%, respectively. This was mainly ascribed to the thicker gradient interface layer, the synergistic effects of GO and CNTs, the rigid and flexible structure, as well as the interfacial interactions and mechanical interlocking effect in the CF-GO-CNTs-PA/resin composite. This work provides a novel concept for the construction of interfaces suitable for advanced CF composites with different structures.