Abstract: To address the poor interfacial adhesion between high-modulus carbon fibers and resin matrices caused by the fibers' high chemical inertness and low surface energy, this paper proposes a novel method for modifying carbon fibers via the cathodic electrochemical grafting of imidazole-based ionic liquids. This study systematically investigated the effects of IL concentration and current density on the physicochemical structure of polyacrylonitrile-based HMCF surfaces and the interfacial properties of the resulting composites. The results indicate that the ILs were successfully grafted onto the acidified carbon fiber surfaces via electrochemical action, establishing a “chemical bridge” between the fiber and the matrix. Specifically, the amino terminals bonded with the oxygen-containing functional groups on the fiber surfaces, while the other ends participated in the curing reaction of the epoxy resin. This dual mechanism significantly improved both the surface wettability and the interfacial bonding strength ofthe carbon fibers. Notably, the optimal modification effect was achieved at an IL concentration of 5wt% and a current density of 25 A·m^-2, where the interfacial shear strength increased from 42.27 MPa (untreated) to 95.52 MPa, representing a remarkable enhancement of 125.9%. This study elucidates the interfacial reinforcement mechanism of electrochemically grafted ILs and provides a novel technical approach for optimizing the interfaces of HMCF com-posites.

Key words: high-modulus carbon fiber, cathodic electrochemistry, ionic liquid, interfacial shear strength