Construction of Inorganic–Organic Interfacial Layer on Carbon Fiber Surface Mediated by Magnesium Ions and Properties of the Corresponding Composites

ABSTRACT Interfacial failure caused by the inherent chemical inertness of carbon fiber surfaces limits the full realization of the high‐performance potential of their composites. In our previous work, we successfully constructed an inorganic–organic interface on carbon fiber surfaces by coordinating the catechol groups in polydopamine (PDA) with weakly electrophilic Mg 2+ ions, thereby effectively enhancing mechanical properties. However, the high cost of dopamine hindered large‐scale industrial production. Inspired by mussel adhesion mechanisms, this study employed the co‐deposition of gallic acid (GA) and polyethyleneimine (PEI) onto carbon fiber surfaces to form a PDA‐like phenol‐amine network coating. This process introduced abundant active groups—such as pyrogallol and amino groups—which provided additional sites for the in situ growth and anchoring of Mg(OH) 2 and enhanced mechanical interlocking between the fiber and the resin. The successful incorporation of the Mg(OH) 2 /(GA‐PEI) three‐dimensional structure was confirmed via SEM, FTIR, and XPS analyses. Following modification, the flexural strength, interlaminar shear strength, and interfacial shear strength of the composites increased by 44.0%, 57.4%, and 105.9%, respectively. This strategy offers a combination of high mechanical performance and low cost, providing a potentially scalable approach for interfacial modification of carbon fibers.