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PUBLISHED ONLINE: 22 JANUARY 2012 | DOI: http://www.nature.com/doifinder/10.1038/nmat3228
Web End =10.1038/NMAT3228
Wetting transparency of graphene
Javad Raee1, Xi Mi2, Hemtej Gullapalli3, Abhay V. Thomas1, Fazel Yavari1, Yunfeng Shi2, Pulickel M. Ajayan3* and Nikhil A. Koratkar1,2*
We report that graphene coatings do not signicantly 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 conrm our measurements and indicate that graphenes wetting transparency is related to its extreme thinness. We also show a 3040% 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.
Graphene is a single-atom-thick sheet of sp2-hybridized carbon atoms arranged in a hexagonal honeycomb lattice. It possesses a unique combination1,2 of high specific surface area, chemical stability, mechanical strength, flexibility, high electrical and thermal conductivity, tunable bandgap, as well as being optically transparent. The optical absorption of a single graphene layer is shown to be 2.3% over the visible spectrum35, which combined with its
high electrical conductivity68 could lead to transparent conductive electrodes911. In spite of intense activity in graphene research, there
are very few reports studying watergraphene interactions1214,
which could be important if graphene is to be used in conformal coatings. Motivated by this, we performed water contact-angle measurements on graphene sheets deposited on a variety of substrates. On surfaces such as copper, gold or silicon, where van der Waals forces control the wetting, we find that graphene remains transparent to the substrate wetting behaviour and remains non-invasive to the substrate/water interface. We call this effect the wetting transparency of graphene. To our knowledge this is the first report of such...