In Situ Synthesis of Self-Assembly Supramolecular Crystal Seeds within Continuous Carbon Nanofibers for Improved Fiber Graphitic Structure

The utilization of carbon-based fibers as a fundamental constituent holds strong appeal for diverse materials and devices. However, the poor fiber graphitic structure resulting from the heat treatment of atactic polyacrylonitrile (PAN) precursors often leads to a modest performance of carbon-based fibers. This paper takes electrospun carbon nanofibers (CNFs) as the research object and provides a seed-assisted graphitization strategy to improve the fiber graphitic structures. The typical melamine/cyanuric acid self-assembly precursor of graphitic carbon nitride is applied as supramolecular seeds in CNFs and demonstrates significant promotion of fiber graphitization, while it decomposes at elevated temperatures. Further studies show that the higher carbon content contributes to the better heat resistance of seeds; thus, nanoscale 2,6-diaminopyridine/cyanuric acid and 2,4,6-triaminopyrimidine/barbituric acid supramolecular seeds are developed. Both systems can be uniformly distributed in PAN precursors through in situ self-assembly and withstand high-temperature carbonization without severe pyrolysis. The dispersed seeds contribute to the formation of fibrillar PAN crystals and promote their conversion to ordered graphitic domains through nucleation and templating roles. The obtained CNFs exhibit increased crystallinity and graphitization degree with improved orientation and refined size of fiber crystals. As a result, the strength, modulus, and elongation at break of CNFs are comprehensively enhanced.