Structural changes of carbon nanotubes in their macroscopic films and fibers by electric sparking processing

Macroscopic films and fibers of chemical vapor deposition (CVD) grown carbon nanotubes (CNTs) were electrically sparked between the nanotube assemblies and the electrode of a direct current power source. Microstructural analyses showed that the electric sparking ablated the ‘hard’ amorphous shells from the CNTs in the film and reshaped them into nanosize particles. This led to the formation of the unique heterostructure of nanoparticle-bonded single-walled carbon nanotubes (SWCNTs) in the sparked film. The ablation of the amorphous shell revealed the inner core of the CVD as-grown nanofiber, which was SWCNT bundles. In case of treating a fiber assembly of purer SWCNT bundles, the electric discharge densified the SWCNTs in the fibers and enhanced their alignment. The selective removal of the amorphous phase from the CNTs in the film is believed to be due to the localized heating generated by sparking. The electric sparking processing could be useful to engineer the structures of CNTs in their macroscopic assemblies, and to reveal the internal structures of the CNTs.