Direct evidence for highly developed graphene in PAN-based carbon fibers

Despite high mechanical properties of nanocarbons, such as graphene, which is believed to be the strongest material, they cannot be sufficiently utilized as structural materials. As an alternative, polyacrylonitrile (PAN)-based carbon fibers are used. In this study, the high mechanical properties of PAN-based carbon fibers were investigated by imaging their nanostructures with atomic resolution. A graphene preparation technique was employed to extract nanostructures within the PAN-based carbon fibers. Lattice fringes with length ˃ 100 nm and width ˃ 10 nm were observed to be significantly larger than the crystallite sizes reported previously. Moreover, a reconstruction image of the basal plane from the Moiré pattern is presented, which shows the turbostratic structure over a large region. It is suggested that the intertwined nature of the crystalline structures transmitted stress between the crystallites and amorphous matrix, which led to the high strength and modulus of the PAN-based carbon fibers. The findings of this study will be useful for enhancing the properties of bulk carbons, which play an important role across numerous industrial fields.