Graphitic carbons have many important applications including electrodes, adsorbents, catalyst support, and solid lubricants. Since the water-graphitic interface is essential to these applications, understanding the interaction between water and graphite is critically important for both fundamental material characterization and practical device fabrication. Recent research interests in graphene and carbon nanotubes over the past decades have brought renewed interests in the water wettability of graphitic carbons. Since 1940s, the prevailing notion on this topic has been that graphitic carbons are hydrophobic, which is supported by many previous water contact angle tests and very well accepted by the community since sp2 carbon is non-polar in nature. However, the recent results1 from our groups showed that graphitic carbons are intrinsically mildly hydrophilic and adsorbed hydrocarbon contaminants from the ambient air render the surface to be hydrophobic. This unexpected finding challenges the long-lasting conception and could completely change the way graphitic materials are made, modeled and modified. With several other research groups reporting similar findings, it is important for the community to realize the importance of airborne contamination on the water wettability of graphitic materials and revisit the intrinsic water-graphite interaction. This presentation aims to summarize our recent work1, 2 on the water wettability of graphitic carbons and discuss future research directions towards understanding the intrinsic water-graphite interaction. Historical perspective will first be provided highlighting the long accepted notion that graphite is hydrophobicity along with a few reports suggesting otherwise. Next, our recent experimental data will be presented showing that pristine graphene and graphite are mildly hydrophilic; FTIR, XPS and ellipsometry characterization showed that hydrocarbons adsorb onto the clean surfaces thus rendering them hydrophobic. These results are further rationalized by analyzing the change in surface energy of the graphitic surfaces before and after hydrocarbon contamination. Then the effect of defects of graphite and the testing methods, e.g., advancing, receding and static contact angles, will be discussed. Lastly, consequences of these findings and future research directions to address a few important unanswered questions will be discussed.

　　References:

　　1. Li, Z.; Wang, Y.; Kozbial, A.; Shenoy, G.; Zhou, F.; McGinley, R.; Ireland, P.; Morganstein, B.; Kunkel, A.; Surwade, S. P.; Li, L. and Liu, H. “Effect of airborne contaminants on the wettability of supported graphene and graphite”, Nature Mater., 2013, 12, 925-931

　　2.Kozbial, A.; Zhou, F.; Li, Z.; Liu, H. and Li, L. “Are graphitic surfaces hydrophobic”, Acc. Chem. Res., 2016, 49(12), 2765-2773.