Wettability and Surface Free Energy of Graphene Films

Abstract

Graphene sheets were produced through chemical exfoliation of natural graphite flake and hydrazine conversion. Subsequently, graphene sheets were assembled into a thin film, and microscale liquid droplets were placed onto the film surface for measurement of wettability and contact angle. It is found that a graphene oxide sheet is hydrophilic and a graphene sheet is hydrophobic. Isolated graphene layers seem more difficult to wet in comparison to graphite, and low adhesion work was found in the graphene-liquid interface. Approximation of solid-liquid interfacial energy with the equation of state theory was applied to determine the graphene surface energy. The results indicate that surface energy of graphene and graphene oxide is 46.7 and 62.1 mJ/m2, respectively, while natural graphite flake shows a surface free energy of 54.8 mJ/m2 at room temperature. These results will provide valuable guidance for the design and manufacturing of graphene-based biomaterials, medical instruments, structural composites, electronics, and renewable energy devices.

Superlubricity of Graphite Induced by Multiple Transferred Graphene Nanoflakes

“…In the case of silica and graphite, their surface energies have been measured at ambient conditions by many researchers, which gives the surface energy of graphite and silica as ${\gamma }_{\mathrm{gra}}^d\approx 54.8\hspace{0.17em}\mathrm{mJ}\hspace{0.17em}{\mathrm{normalm}}^{-2}$ and ${\gamma }_{{\mathrm{sio}}_2}^d\approx 600\hspace{0.17em}\mathrm{mJ}\hspace{0.17em}{\mathrm{normalm}}^{-2}$ 18. Thus, the interfacial energy between silica and graphite can be calculated as W gra‐sio2 ≈ 363 mJ m −2 .…”

Construction of Efficient 3D Gas Evolution Electrocatalyst for Hydrogen Evolution: Porous FeP Nanowire Arrays on Graphene Sheets

“…As illustrated in Scheme 1 , FeSO 4 ·7H 2 O was first dissociated in a mixture containing deionized water (DI) water and glycerol. It was then converted to ferric ions which were attached to the neutral glycerol ligands during the hydrolysis process11 When GO was employed as a support and dispersed into the solvents, the polar glycerol solute uniformly attached onto the surface of the GO sheets to form a glycerol quasi‐emulsion coated film 12. Most α‐FeO(OH) active nucleation sites are then generated on the surface of the glycerol coated GO nanosheets by heterogeneous nucleation at the beginning of the hydrolysis process.…”

Evaporation induced wrinkling of graphene oxide at the nanoparticle interface

“…GO is hydrophilic due to its rich oxygenated groups and its water contact angle is reported to be ~67. 36 Although freshly cleaved graphene was reported to be hydrophilic (contact angle smaller than 90), 37 our graphene was made by chemical reduction and has been exposed to air for a long time. Therefore, it should be hydrophobic.…”