Controllable Fabrication of Flexible and Foldable Carbon Nanofiber Films

Abstract Carbon nanofibers (CNFs) fabricated through traditional methods are generally composed of amorphous carbon and graphite sheets, which usually endow CNFs with high modulus and brittleness. Here, a strategy of controlling graphite sheet structures in CNFs for the scalable fabrication of silk‐like flexible CNF films that can be arbitrarily folded in any shape and can undergo thousands of dynamic bending deformation cycles is reported. In detail, the carbon precursor of polyacrylonitrile (PAN) is first electrospun into NFs and then by controlling the pre‐oxidation reaction and carbonization process to design CNFs with different graphitization degrees, flexible CNF films with tunable mechanical properties from the traditional bending resilience flexibility to truly foldable flexibility can be fabricated. Meanwhile, a correlation mechanism between microstructure and the foldable flexibility of CNFs is proposed. Importantly, it is found that manipulating the pre‐oxidation temperatures of precursor PAN NFs can effectively reduce the structural stiffness of CNFs due to the appropriate number of graphene sheets. This study provides a theoretical basis for designing truly foldable CNF films for multiple applications.