Control of Super Hydrophobic and Super Hydrophilic Surfaces of Carbon Nanowalls Using Atmospheric Pressure Plasma Treatments

Super hydrophobic and super hydrophilic surface treatment methods for carbon nanowalls (CNWs) which are carbon nanostructures consisting of stacks of graphene sheets vertically standing on substrates and having ultra high aspect ratios of over 50, were developed using atmospheric pressure plasma, and their mechanisms were discussed on the basis of the elemental compositions of surfaces. The contact angle of water droplet on CNWs markedly decreased from 137.3 to 6.2° with the atmospheric pressure plasma treatments using Ar gas. This indicates the super hydrophobic and super hydrophilic transition of CNW surfaces. Although a morphological change was hardly found, the surface compositions of fluorine and oxygen atoms markedly changed after the plasma treatment for only 5 s. Furthermore, the treatment time dependence of the surface tension of CNWs indicates two different mechanisms at earlier and later stages of surface modification using atmospheric pressure plasma.