Enhancing the Interfacial Performance of Composites via the Construction of a Multiscale Rigid‐Flexible Interfacial Layer on Carbon Fiber Surfaces

ABSTRACT Through electrostatic self‐assembly, positively charged polyethyleneimine (PEI) and negatively charged carboxylated multi‐walled carbon nanotubes (CNT‐COOH) were sequentially formed onto oxidized carbon fiber (CF) surfaces, creating a multiscale “PEI‐CNT” reinforcement layer. The results indicated that a CNT solution concentration of 2 mg/mL yielded the most homogeneous distribution of nanotubes on the fiber surface. This modification substantially enhanced the CF's surface chemical activity and wettability. Compared to unmodified CF composites, the interfacial shear strength (IFSS) of CF‐PEI‐2CNT/EP rose by 101.70%, attributed to enhanced chemical bonds and mechanical interlocks at the fiber–resin interface. In addition, molecular dynamics simulations were employed to evaluate the fiber–matrix interfacial strength. The simulation results revealed a progressive increase in interfacial energy throughout the fiber modification process, aligning with the experimental findings. Mean square displacement (MSD) analysis revealed that post‐modification, the fiber–resin adsorption capacity increased significantly, while the resin's mobility decreased. Radial distribution function (RDF) analysis revealed enhanced hydrogen bonding at the fiber‐resin interface, directly correlating with improved interfacial adhesion. This research employs an integrated methodology of empirical analysis and computational modeling to comprehensively demonstrate the notable improvement of interfacial properties in CF/epoxy composites. This innovative interfacial design strategy offers valuable insights for interfacial optimization in other composite materials.