Hydrophilicity of Graphene in Water through Transparency to Polar and Dispersive Interactions.

Establishing contact angles on graphene-on-water has been a long-standing challenge as droplet deposition causes free-floating graphene to rupture. The current work presents ice and hydrogels as substrates mimicking water while offering a stable support for graphene. The lowest water contact angles on graphene ever measured, namely on graphene-on-ice and graphene-on-hydrogel, are recorded. The contact angle measurements of liquids with a range of polarities allow the transparency of graphene toward polar and dispersive interactions to be quantified demonstrating that graphene in water is hydrophilic. These findings are anticipated to shed light on the inconsistencies reported so far on the wetting properties of graphene, and most particularly on their implications toward rationalizing how molecules interact with graphene in water.