Significantly enhancing CFRP/titanium joint bonding strength using a novel PDA-Fe organic nanoparticle precoating

To address the inadequate bonding strength between machined carbon fiber reinforced polymer (CFRP) and metal, this study investigates a novel precoating treatment utilizing organic nanoparticles. Leveraging the synergistic effect between the silane coupling agent (3-aminopropyl) triethoxysilane (APS) and polydopamine-chelated iron nanoparticles (PDA-Fe), a dense protective layer forms on the damaged CFRP surface. Single lap shear (SLS) tests demonstrated a significant 93 % increase in shear strength for joints with APS-(PDA-Fe) treated CFRP. Comparative studies with inorganic particles—multi-walled carbon nanotubes (MWCNTs), zinc oxide (ZnO), and silica (SiO 2 )—revealed that APS-(PDA-Fe) yielded the highest bonding strength enhancement for milled CFRP. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), surface wettability analysis, and microscopic morphology characterization elucidated the underlying mechanism: the formation of a protective encapsulating layer that repairs and reinforces damaged fibers, combined with abundant polar functional groups (e.g., hydroxyl, amino, quinone) in APS and PDA-Fe, which substantially enhance resin adhesion to the CFRP surface.