Structures and characterizations of bundles of collapsed double-walled carbon nanotubes

The performance of carbon nanotube fibers (CNTFs) significantly depends on the packing styles of carbon nanotube (CNT) bundles. Revealing the structures and characterizations of CNT bundles is contributive to understanding the structures, properties and even the formation of CNTFs during chemical vapor deposition (CVD) processing. In this paper, bundles consisting of collapsed double-walled carbon nanotubes (CDWNT) in continuous CNTFs fabricated from CVD processing were characterized and analyzed by transmission electronic microscopy (TEM) and x-ray diffraction (XRD). TEM observations show that the continuous CNTFs are composed of CDWNT-bundle units. CDWNT- bundle units of 10-20 nm in thickness contain near numbers of collapsed tubes. The degree of collapse of the CDWNTs varies with their location in the bundle and their own diameter. CDWNT- bundle units pack side by side or face to face, assembling into super-bundles with diameters of 200-300 nm. XRD patterns show that three novel and strong peaks appear at 10 degrees-15 degrees, 21.3 degrees and 23.7 degrees, respectively, corresponding to CDWNT two side pores (10 degrees-15 degrees) and CDWNT layers (21.3 degrees and 23.7 degrees), which indicates the collapsed tube structures in CNTFs are common characterizations. Finally, a collapse mechanism is discussed from the observation and analysis.