An effective method for manufacturing hollow carbon nanofibers and microstructural analysis

Hollow carbon nanofibers (HCNFs) were successfully manufactured by co-axial (core/shell) electrospinning of poly(styrene-co-acrylonitrile) (SAN) and poly(acrylonitrile) (PAN) solutions. The shell component (PAN) was converted into a turbostratic carbon structure by thermal treatment, whereas the sacrificial core component (SAN) was eliminated. SAN was found to be a very suitable material for the sacrificial core. SAN exhibited excellent co-axial electrospinnability to produce a uniform core/shell nanofiber precursor because of its immiscibility with PAN. Also, SAN had a good thermal sustainability that prevented the PAN shell from shrinking during the stabilization and carbonization processes, thus maintaining the shell structure. These two predominant properties of SAN enabled the manufacturing of uniform HCNFs with controlled inner diameters and wall thickness that ranged from 120-510 nm and 52-145 nm, respectively. The core solution properties, such as solution concentration and flow rate, were mostly effective in controlling both the outer diameters and the wall thicknesses of HCNFs. The microstructure of these HCNFs was investigated using high resolution transmission electron microscopy. The crystallite size and crystallinity of HCNFs were dependent on their wall thicknesses. As the wall thicknesses of HCNFs decreased, they developed smaller crystallites and higher crystallinities.