Formation mechanism of micrometer-sized carbon tubes

Micrometer-sized carbon tubes and their regularly assembled structures can be easily prepared via the pyrolysis of composite fibers consisting of a poly(ethylene terephthalate) (PET) core and a conducting polymer skin layer, such as polypyrrole (PPy). Using this new chemical approach, the diameter, wall thickness, and length of carbon tubes can be effectively controlled. The formation mechanisms of the PPy/PET composite fibers and their corresponding carbon tubes have been studied with the aid of various spectroscopic and analytical methods. The investigations indicated that the morphological quality, integrity, and thickness of the PPy coating layer are the most crucial properties in determining the success of obtaining hollow and opened carbon tube structures. Observations with SEM on the pyrolyzed samples indicated that the PET core of a composite fiber started to melt between 230 and 290 degreesC and then decomposed and almost disappeared at ca. 390 degreesC, leaving behind only the hollow sheath. Both the diameter and wall thickness of such hollow tube further decreased as the treatment temperature elevated during the subsequent carbonization stage. The released gaseous, as well as the sublimed solid, byproducts during the carbon tube formation process were also monitored and investigated. All results of the present study indicate that PPy is thermally more stable than PET, thus suggesting that the carbon tube walls were mainly derived from the PPy skin layers.