Wetting of CVD Carbon Films by Polar and Nonpolar Liquids and Implications for Carbon Nanopipes

The handling, dispersion, manipulation, and functionalization of carbon nanotubes and nanopipes often require the use of solvents. Therefore, a good understanding of the wetting properties of the carbon nanotubes is needed. Such knowledge is also essential for the design of nanotube-based nanofluidic devices, which hold the promise of revolutionizing chem. anal., sepn., drug delivery, filtration, and sensing. In this work, we investigated the wetting behavior of individual nanopipes produced by the chem. vapor deposition (CVD) of carbon in porous alumina templates and of thin carbon films produced by the same technique. The carbon pipes and films have the same chem. and structure as detd. by Raman and IR spectroscopies and, when similarly treated, demonstrate the same qual. wetting behavior, as detd. by optical microscopy. Thus, measurements conducted on the carbon film surface are relevant to the nanopipes. In the case of the nanopipes, filling with various liqs. was monitored. Contact angle expts. with both polar (water, glycerol, ethylene glycol, ethanol, tetra-hydro furan, and 2-propanol alc.) and nonpolar liqs. (cyclohexane, hexadecane, poly(dimethylsiloxane), and a fluoro-silicone) were conducted on films using the sessile drop method. The contact angles on the CVD carbon films ranged from 0 to 79 Deg. The exposure of the carbon films to a NaOH soln., typically used to dissolve the alumina template, led to a significant decrease of the contact angle, esp. in the case of polar liqs.