(333g) Wetting Transparency of Graphene on Hydrogel

The water wettability of a solid surface is determined by the solid material and, therefore, is usually changed by either using a different solid material or applying a coating. However, recent research has suggested that water can (at least partially) “see through” an atomic-thick graphene layer, giving rise to the so-called “wetting transparency” effect. This interesting finding provides tremendous opportunity since it means that the wettability of an atomic-thick film can be tuned by selecting an appropriate supporting substrate. The picture becomes even more appealing if the substrate is a liquid instead of a solid, since one can readily change the liquid underneath the graphene, thereby providing real-time control of the surface wettability, a capability highly desirable in many applications. Nevertheless, research to date has almost exclusively focused on the solid substrates and very little is known about the wettability of graphene on liquid substrates. One of the key reasons for that is macroscopic water droplets rupture the graphene supported by a liquid such as water.

Here we report our experimental results on the wetting transparency of graphene supported by a hydrogel. The key advantage of using a hydrogel support is that it contains mainly (e.g., 96%) water yet is mechanically robust enough to support the graphene in the contact angle measurements. The single-layer graphene on Cu grown by chemical vapor deposition (CVD) has been etched and then transferred onto the agarose hydrogel. The Raman spectrum of graphene indicates the high quality of graphene on the hydrogel. The contact angles (CA) of two commonly used testing liquids, water and diiodomethane, on both bare hydrogel and graphene/hydrogel suggest that graphene is almost complete wetting transparent, i.e., the CA of the hydrogel is very close to that of graphene/hydrogel. The possible mechanisms for the observed wetting transparency will also be discussed.