Abstract
We report that graphene coatings do not significantly disrupt the intrinsic wetting behaviour of surfaces for which surface–water interactions are dominated by van der Waals forces. Our contact angle measurements indicate that a graphene monolayer is wetting-transparent to copper, gold or silicon, but not glass, for which the wettability is dominated by short-range chemical bonding. With increasing number of graphene layers, the contact angle of water on copper gradually transitions towards the bulk graphite value, which is reached for ~6 graphene layers. Molecular dynamics simulations and theoretical predictions confirm our measurements and indicate that graphene’s wetting transparency is related to its extreme thinness. We also show a 30–40% increase in condensation heat transfer on copper, as a result of the ability of the graphene coating to suppress copper oxidation without disrupting the intrinsic wettability of the surface. Such an ability to independently tune the properties of surfaces without disrupting their wetting response could have important implications in the design of conducting, conformal and impermeable surface coatings.
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Acknowledgements
N.A.K., P.M.A. and Y.S. thank the Advanced Energy Consortium (AEC) for funding support. N.A.K. also acknowledges funding from the USA National Science Foundation (Awards CMMI-1130215 and CBET-0853785). P.M.A. also acknowledges support from the ONR graphene MURI program. We thank Y. Peles at RPI for providing us access to the condensation heat-transfer test facility in his Lab.
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N.A.K. and P.M.A. designed and directed the research. J.R. performed the wetting measurements and optical microscopy. H.G. fabricated the graphene samples on the various substrates. F.Y. performed the Raman characterization of the samples. A.V.T. and N.A.K. performed the condensation heat-transfer measurements. X.M. and Y.S. performed the MD simulations. X.M., Y.S. and N.A.K. carried out the continuum modelling. N.A.K., P.M.A. and Y.S. wrote the paper.
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Rafiee, J., Mi, X., Gullapalli, H. et al. Wetting transparency of graphene. Nature Mater 11, 217–222 (2012). https://doi.org/10.1038/nmat3228
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DOI: https://doi.org/10.1038/nmat3228
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