Graphene Drape Minimizes the Pinning and Hysteresis of Water Drops on Nanotextured Rough Surfaces

Abstract

Previous studies of the interaction of water with graphene-coated surfaces have been limited to flat (smooth) surfaces. Here we created a rough surface by nanopatterning and then draped the surface with a single-layer graphene sheet. We found that the ultrasheer graphene drape prevents the penetration of water into the textured surface thereby drastically reducing the contact angle hysteresis (which is a measure of frictional energy dissipation) and preventing the liquid contact line from getting pinned to the substrate. This has important technological implications since the main obstacle to the motion of liquid drops on rough surfaces is contact angle hysteresis and contact line pinning. Graphene drapes could therefore enable enhanced droplet mobility which is required in a wide range of applications in micro and nanofluidics. Compared to polymer coatings that could fill the cavities between the nano/micropores or significantly alter the roughness profile of the substrate, graphene provides the thinnest (i.e., most sheer) and most conformal drape that is imaginable. Despite its extreme thinness, the graphene drape is mechanically robust, chemically stable, and offers high flexibility and resilience which can enable it to reliably drape arbitrarily complex surface topologies. Graphene drapes may therefore provide a hitherto unavailable ability to tailor the dynamic wettability of surfaces for a variety of applications.

Graphene-coated meshes for electroactive flow control devices utilizing two antagonistic functions of repellency and permeability

“…The CA of water droplets on both bare Ni mesh and GCNM are nearly identical, as shown in Supplementary Fig. 5, demonstrating the wetting transparency2122232425 of the graphene coating on the metal substrates. To evaluate the protective effect of graphene against thermal oxidation, we thermally annealed both GCNM and bare Ni mesh at 400 °C for 4 h. After the thermal annealing process, the colour of the bare Ni mesh significantly changed from silver to dark blue, whereas the colour of the graphene-coated samples remained unchanged.…”

“…In fact, the wetting transparency effect can also be extended to strongly hydrophobic (that is, rough) substrates24, if the graphene coating is deposited in-situ via chemical vapour deposition (CVD) and conforms to the surface roughness features of the substrate. These results indicate that graphene-coated metal substrates can be used as water harvesting devices with greatly improved anti-oxidation and anti-corrosion capabilities, without disrupting the intrinsic wettability of the underlying substrate2122232425. However, previous studies only investigated the passive wettability of graphene and graphene hybrid composites; to the best of our knowledge, active control of the wettability of graphene-coated surfaces has not been investigated thus far.…”

“…Interestingly, recent progress reveals that monolayer graphene is wetting-transparent212223 to an underlying substrate provided that the substrate is significantly more wettable (hydrophilic) than the graphene. In fact, the wetting transparency effect can also be extended to strongly hydrophobic (that is, rough) substrates24, if the graphene coating is deposited in-situ via chemical vapour deposition (CVD) and conforms to the surface roughness features of the substrate.…”

Droplets impact on textured surfaces: Mesoscopic simulation of spreading dynamics

“…5b), the bigger one is advancing angle  A and the smaller one is receding angle  R , again, the difference between them can be seen as contact angle hysteresis. A few of theoretical analyses and experiments [6,[12][13][14][15][16][17][18] show that droplets in Cassie state can provide smaller contact angle hysteresis as well as larger contact angle. Hence for many industrial applications, such as self-cleaning surfaces, people show more interests in this droplet state.…”

“…Hence for many industrial applications, such as self-cleaning surfaces, people show more interests in this droplet state. Eklavya et al [16] draped the nanotextured surface with a single-layer graphene sheet to avoid the water intruding into the textured surfaces and in the meantime hold the droplet in an ideal Cassie state. Their experiments showed that the droplet separated by the graphene sheet could hardly be pinned to the substrate and the contact angle hysteresis was reduced significantly.…”