title: Wetting transparency of graphene.
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.
authors.affiliation: Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, USA.
authors.forename: Javad
authors.initials: J
authors.lastname: Rafiee
authors.forename: Xi
authors.initials: X
authors.lastname: Mi
authors.forename: Hemtej
authors.initials: H
authors.lastname: Gullapalli
authors.forename: Abhay V
authors.initials: AV
authors.lastname: Thomas
authors.forename: Fazel
authors.initials: F
authors.lastname: Yavari
authors.forename: Yunfeng
authors.initials: Y
authors.lastname: Shi
authors.forename: Pulickel M
authors.initials: PM
authors.lastname: Ajayan
authors.forename: Nikhil A
authors.initials: NA
authors.lastname: Koratkar
mesh_terms: D006108:Graphite / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D056004:Molecular Dynamics Simulation; D012825:Silicon / Q000737:chemistry; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D006108:Graphite; D012825:Silicon