Mussel-inspired ferric ion-polydopamine complex as a facile, green and efficient platform to functionalize carbon fiber for improving interfacial adhesion of composites

A mussel inspired co-deposition of ferric ion-polydopamine (PDA) is explored and constructed on carbon fiber via facile dip-coating strategy for the first time to realize the enhancement in interfacial adhesion of epoxy composites. Varied contents of ferric ion are designed to allow comparison how the contents of formed complexes affect the surface characteristics of fiber and interfacial adhesion of composites. Compared with pure PDA modified fiber, the size and number of PDA nanospheres attached on fiber first declines distinctly and then increases as the addition level of ferric ions raises, but the coordination product of both bis-and tris-Fe3+-catechol complexes exist, only the yield of complexes varies with the addition amount of FeCl3. This indicates that the level of Fe3+ ions obviously impact DA oxidation, not the complex product. Increments in interfacial shear strength across all ferric ion-PDA complex modified fibers are noticed, associating with the stronger Fe3+…O coordination bonds that could enhance the interfacial crosslinking density. However, the optimal IFSS is attainable when appropriate amount of Fe3+ ions were added, which endows the fiber with good resin wettability. The ferric ion-PDA complex assisted surface modification demonstrated to be an effective and feasible avenue in interphase tuning of fiber reinforced composites, which could be also anticipated to extend to other metallic ion-PDA complexes.