Doping-Induced Tunable Wettability and Adhesion of Graphene

We report that substrate doping-induced charge carrier density modulation leads to the tunable wettability and adhesion of graphene. Graphene's water contact angle changes by as much as 13 degrees as a result of a 300 meV change in doping level. Upon either n- or p-type doping with subsurface polyelectrolytes, graphene exhibits increased hydrophilicity. Adhesion force measurements using a hydrophobic self-assembled monolayer-coated atomic force microscopy probe reveal enhanced attraction toward undoped graphene, consistent with wettability modulation. This doping-induced wettability modulation is also achieved via a lateral metal graphene heterojunction or subsurface metal doping. Combined first principles and atomistic calculations show that doping modulates the binding energy between water and graphene and thus increases its hydrophilicity. Our study suggests for the first time that the doping-induced modulation of the charge carrier density in graphene influences its wettability and adhesion. This opens up unique and new opportunities for the tunable wettability and adhesion of graphene for advanced coating materials and transducers.