Synergistic Strengthening and Toughening the Interphase of Composites by Constructing Alternating “Rigid‐and‐Soft” Structure on Carbon Fiber Surface

Abstract Interphase with nacre‐like structured multilayer is constructed by alternatively depositing two polymers, respectively “rigid” polydopamine (PDA) and “flexible” polyether amine, on carbon fiber surface via the layer‐by‐layer (LbL) approach. The optimal interfacial strength and toughness are achieved for composites with three layers of PDA/polyether amine, respectively, 39.2% and 99.8% superior to the untreated fiber composites. The outstanding mechanical properties are mainly ascribed to the synergistic interactions of covalent bond, hydrogen bonding, and π–π stacking among fiber, multilayer, and matrix by transferring stress and bridging cracks, as well as the alternating “rigid and flexible” structure of interphase by deflecting crack path and inducing plastic deformation and viscoplastic energy dissipation. This work opens a new, feasible, and easy scalable avenue for constructing integrated high‐performance fiber composites.