Effect of Graphitization on the Wettability and Electrical Conductivity of CVD-Carbon Nanotubes and Films

The use of carbon nanomaterials in various applications requires precise control of their surface and bulk properties. In this paper, we present a strategy for modifying the surface chem., wettability, and elec. cond. of carbon tubes and films through annealing in a vacuum. Expts. were conducted with 60-300 nm nanotubes (nanopipes), produced by noncatalytic chem. vapor deposition (CVD) in a porous alumina template, and with thin films deposited by the same technique on a glassy carbon substrate having the same structure and chem. of the CNTs. The surface of the as-produced CVD-carbon, treated with sodium hydroxide to remove the alumina template, is hydrophilic, and the bulk elec. cond. is lower by a factor of 20 than that of fully graphitic multiwalled nanotubes (MWNT) or bulk graphite. The bulk elec. cond. increases to the cond. of graphite after annealing at 2000 DegC in a high vacuum. The anal. of CNTs by transmission electron microscopy (TEM) and Raman spectroscopy shows the ordering of carbon accompanied by an exponential increase of the in-plane crystallite size, La, with increasing annealing temp. Environmental SEM (ESEM) was used to study the interaction of CNT with water, and contact angle measurements performed using the sessile drop method on CVD-carbon films demonstrate that the contact angle increases nearly linearly with increasing annealing temp.