Two-stage mechanical percolation in the epoxy resin intercalated buckypaper with high mechanical performance

Buckypaper is a superb material for translating the exceptional properties of carbon nanotubes (CNTs) into the macroscopic scale. However, its poor mechanical properties severely limit its performance for larger scale applications, due to the weak intertube interactions. A given small content of epoxy resin is intercalated into the porous CNT network in order to enhance the intertube interactions. An extremely high enhancing efficiency for both Young's modulus (similar to x 20) and ultimate strength (similar to x 26) of the buckypaper, and a novel two-stage mechanical percolation behaviour are observed. This is ascribed to the relative small molecular dimensions of the epoxy resin, with which the epoxy resin can diffuse into the nano-sized intertube gaps much more effectively. A molecular dynamics (MD) simulation conducted reveals that the epoxy resin tends to congregate at the CNT junctions, and has a strong effect in enhancing the intertube stress transfer abilities. Moreover, an analytical calculation based on the MD simulation and the fracture surfaces of the buckypaper strips establishes that the two-stage mechanical percolation behaviour is dominated by the epoxy diffusion behaviours. This work offers an innovative nano-engineering approach to enhance the mechanical properties, as well as other functionalities, of the buckypaper, which is important for its potential applications.