Understanding wettability changes from practical plasma functionalization of carbon nanotubes

Combining continuous wave and pulsed plasma modes enables strong interfacial bonding of high levels of desired surface functional groups. The method has been applied to a thin film of multiwalled carbon nanotubes, a nanostructured and relatively inert material, using N₂ + H₂ plasma. A high density of primary amine groups (~2.6%) was achieved without damaging the tube surface. Contact angle measurements, using different probe liquids, plus model calculations of surface energy agree well with the spectroscopy and electron microscope results, i.e., the polar part shows significant changes while the non-polar part was unchanged. These results indicate that the wettability changes in the thin film of carbon nanotubes by the plasma treatment are due to the changes in surface chemistry. This confirms the effectiveness and practicality of the improved plasma method that should greatly help the use of nanotubes in applications from biomaterials to nanocomposites.