Study on the Surface Energy of Supported Graphene By Contact Angle Measurements

Due to the atomic thinness of graphene, its integration into a device will always involve its interaction with at least one supporting substrate, making the surface energy of graphene critical to its fabrication and real-life applications. In the current work, the contact angle of graphene synthesized by chemical vapor deposition (CVD) was monitored temporally after synthesis using water, diiodomethane, ethylene glycol, and glycerol.  The surface energy was then calculated based on the contact angle data by Fowkes, Owens-Wendt (extended Fowkes), and Neumann models. The surface energy of fresh CVD graphene grown on a copper substrate (G/Cu) immediately after synthesis was determined to be 62.2 mJ/m² (Fowkes), 53.0 mJ/m² (Owens-Wendt) and 63.8 mJ/m² (Neumann), which decreased to 45.6 mJ/m², 37.5 mJ/m² and 57.4 mJ/m², respectively, after 24 hours of air exposure. The ellipsometry and ATR-FTIR characterization indicates that the surface energy of G/Cu is affected by airborne hydrocarbon contamination. G/Cu exhibits the highest surface energy immediately after synthesis and the surface energy decreases gradually after airborne hydrocarbon contamination occurs.  The intrinsically mild polarity of G/Cu surface has been discussed and could be attributed to high-energy surface defects, pi-hydrogen bonding, and partial wetting transparency.