Influence of surface morphology on the wettability of cluster-assembled carbon films

We have evaluated the surface energy and characterized the wettability of cluster-assembled carbon films deposited on polyethylene, Si and Al substrates by a sessile-drop method using water and glycerol. The effective surface energy of nanostructured carbon is of the order of 30 mJ/m(2) as calculated using the Fowkes approach. The advancing contact angle (66-83degrees) is found to increase with surface roughness, i.e. the surface becomes more hydrophobic as the roughness increases. This behavior is ascribed to gas trapping in pores of the film with a self-affine surface. It is argued that the wettability of nanostructured carbon and other cluster-assembled coatings can be tuned simply by controlling the surface topography, through a suitable control of the deposition parameters, such as the cluster size distribution.