Development of a "Rigid-Flexible" Structure at the Interface Through Aramid Nanofibers@MXene to Enhance Mechanical Properties of Carbon Fiber/Polyamide Composites.

With the increasing development of nanomaterials, the construction of multiscale nanostructured interphase has emerged as a viable technique to reinforce carbon fiber-reinforced polymer composites. Here, "flexible" aramid nanofibers (ANFs) were first introduced on the surface of carbon fibers (CF) by electrophoretic deposition (EPD), and then "rigid" MXene sheets were grafted by ultrasonic impregnation. This feasible two-step treatment introduces a hierarchical "rigid-flexible" structure at the CF/polyamide (PA) interface. Results showed that this "rigid-flexible" multilayer structure improved the roughness, chemical bonding, mechanical interlocking, and wettability of CF/PA composites. At the same time, the modulus variation between the fiber and the matrix is significantly smoothed due to the increased thickness of the interfacial layer, increasing the payload transfer from the PA matrix to the fiber and decreasing the stress concentration. Compared to the desized CF, the interlaminar shear strength (ILSS) and tensile strength of the modified CF-ANF@MX/PA composite increased by 50.02 and 36.11%, respectively. This innovative interfacial design and feasible treatment method facilitate the construction of firmly interacting interfacial layers in CF/PA composites, offering broad prospects for the production of high-performance CF/PA composites.