Influence of Precursor\nStructure on the Formation\nof Active Carbon Deposition Sites and Helical Graphite Cones Growth\nMechanism

Graphite cones (GCs) have large aspect ratios and high\nmechanical\nproperties, which have attracted much attention due to their similarity\nto carbon nanotubes and vapor-grown carbon fibers. Currently, there\nhave been some preparation methods and growth mechanisms for GCs.\nStill, the growth conditions of GCs have not been explored from the\nperspective of the molecular structure of the precursor. Therefore,\nthis paper is based on the in situ preparation of helical graphite\ncones (HGCs) using different precursors of polyimide (PI) graphite\nfibers (GFs) doped with polycyclic aromatic hydrocarbons (PAH). By\nvarying the type of precursor of PI fibers, it can be found that HGCs\nappeared on GFs with pyromellitic dianhydride/4, 4′-oxidiamine\n(PMDA/ODA), and biphenyl tetracarboxylic dianhydride/4, 4′-oxidiamine\n(BPDA/ODA) as precursors, but there is no growth of HGCs on GFs with\nbiphenyl tetracarboxylic dianhydride/<i>p</i>-phenylenediamine\n(BPDA/PDA) as precursors. Based on this phenomenon, it can be further\ndiscovered that the growth of HGCs is related to the ether-oxygen\nbonds in the ODA. The ether-oxygen bonds broken during heat treatment\nprovide active carbon deposition sites, which is a key factor for\nthe growth of HGCs, thus producing many HGCs. The discovery at the\nmolecular structure level significantly impacts the future preparation\nof HGCs and the improvement of their growth mechanisms.