(485c) Water Wettability of Graphitic Surface: Contaminants, Defect and Roughness

Since 1940, it has been long accepted that the graphite is hydrophobic. Our recent experimental results indicated that the long-established hydrophobicity of graphitic surfaces actually results from airborne hydrocarbon contamination. A fresh graphitic surface is indeed mildly hydrophilic and the adsorption of airborne hydrocarbons renders the surface to be hydrophobic. Though the finding has been confirmed by several other research groups, there are still unanswered questions. Since the wettability of ta solid surface is affected by both defects and surface roughness, it is essential to clarify the effect of these two parameters. In this presentation, we report our experimental results on how the defect and roughness impacts the intrinsic water wettability of graphitic surface. The water wettability of clean graphite/graphene was studied using water contact angle (WCA) measurements. The defect densities and topography of the graphitic surfaces were characterized by Raman spectroscopy and AFM. Wenzel model has been utilized to relate the surface roughness to the water wettability. A qualitative model is proposed to explain the effect of defects Based on the model and the experimental results. The experimental results showed that, taken the defects and roughness into consideration, the graphitic surface is intrinsically mildly hydrophilic.