Nautilus-inspired MXene@TiO2 brick-mortar architecture towards superior strength-toughness balance in carbon fiber/epoxy composite

Balancing strength and toughness with synergistic enhancement remains a critical challenge in developing high-performance carbon fiber (CF) composites. Deep-sea nautilus exhibits a superior strength-toughness balance compared with shallow-water nacre, attributed to its exceptionally large platelet aspect ratio, densely distributed nano-asperities, and higher organic matrix content that jointly give rise to enhanced interfacial shear resistance through coupled adhesion-friction mechanisms. Inspired by this naturally optimized architecture, we develop a biomimetic “brick-and-mortar” interphase using MXene@TiO 2 assembled with polydopamine/polyethyleneimine (PDA/PEI) nanolayers. Unlike conventional “brick-and-mortar” interphases, the micro-convex TiO 2 nanoparticles on MXene surfaces provide mechanical interlocking and more homogenized stress transfer, while PDA/PEI layers ensures strong chemical adhesion, enabling the simultaneous enhancement of interfacial strength and toughness. The resulting CF-MXene@TiO 2 /epoxy composite exhibits a 66.9 % increase in interfacial shear strength (75.6 ± 3.3 MPa) and a 71.9 % rise in interfacial fracture toughness G ic  = 91.3 ± 5.9 J/m 2 , compared to the desized CF. Flexural strength and interlaminar shear strength are also improved by 31.6 % and 46.9 %, respectively. Mechanistic analysis indicates that the synergistic interaction between the micro-convex “brick” (MXene@TiO 2 nanosheet) and the “mortar” (PDA/PEI nanolayer) optimizes the interfacial microstructure, effectively suppressing crack propagation and promoting superior interfacial strength and toughness. This work provides a rational biomimetic strategy to overcome the strength-toughness trade-off and offers potential applications in aerospace, marine, and other high-performance CF composite structures.