All-carbon multi-scale and hierarchical fibers and related structural composites: A review

Recent advancements in the preparation of all-carbon multi-scale fibers and their use in carbon fiber (CF)-reinforced polymer composites are reviewed. A multi-scale or hierarchical structure is the result of a combination of micro-scaled fibers and nano-scaled fillers which are in intimate contact by physical or chemical interactions. Carbonaceous nanofillers, such as carbon black, carbon nanotubes and nanofibers, graphene and its oxidized derivatives, can be deposited on CFs by different strategies. In particular, preformed nanoparticles (indirect methods) or in situ prepared nanoparticles (direct methods) can be used. Multi-scale structuring of the interlaminar region via various deposition techniques is also discussed. An overview of multi-scale fibers and multi-scale structured interlaminar layers to improve the load transfer between the matrix (namely thermoset-, thermoplastic- and carbon-based) and the reinforcing (CFs) phase is considered for this review. Moreover, their use to add new functionalities (electric conductivities, sensing, thermal conductivities) to structural composites is also reviewed. Finally, the recent efforts in modeling the mechanical behavior of the interphase and interlaminar regions of all-carbon composites with multi-scale fibers are discussed, along with some notes on future challenges.