Wetting translucency of graphene on plasmonic nanohole arrays

Graphene- a carbon allotrope with atoms arranged in monolayer 2D hexagonal lattice- exhibits wide range of applications in batteries, supercapacitors, solar cells, biosensing, light-emitting diodes, semi-conductors, materials composites, and coatings to name a few. Significant progress has been made to understand the electronic, mechanical, and optical characteristics of graphene. However, the wettability of graphene, which is important for surface modification and thermal/fluidic properties, is still not well understood. The level of transparency to van der Waals forces, chemical bonds, and electrostatic interactions between atoms and molecules on two sides of graphene single layer is partially known. Static contact angle between the edge of sessile drop and functionalized surface provides surface tension value based on Owens–Wendt model and is important for wettability studies. In this work, we investigate the surface energy of glass, silicon wafer, and plasmonic nano-hole arrays (Silver, Polymer and Gold) suspended with CVD grown and transferred single layer of graphene. Our experimental results demonstrate that graphene is wetting transparent in the case of silicon and wetting opaque when deposited on the glass. The plasmonic nanohole arrays (NHAs) fall in the partially wetting transparent category. On plasmonic NHAs, the surface energy value got reduced with the suspending single layer graphene compared to absence of graphene. These results showed that the underlying substrate does affect the wettability of graphene monolayer due to van der Waal hydrocarbon, metal-carbide, and silica-carbon bonding which tends to provide deeper understanding of the wetting dynamics. This study elucidates the mechanism of short-range forces between water-graphene-substrate which is important during the fabrication of adhesives and coatings with controlled fluidic and heating properties. (letter)