Study on the Surface Energy of Graphene by Contact Angle Measurements

Abstract

Because of the atomic thinness of graphene, its integration into a device will always involve its interaction with at least one supporting substrate, making the surface energy of graphene critical to its real-life applications. In the current paper, the contact angle of graphene synthesized by chemical vapor deposition (CVD) was monitored temporally after synthesis using water, diiodomethane, ethylene glycol, and glycerol. The surface energy was then calculated based on the contact angle data by the Fowkes, Owens-Wendt (extended Fowkes), and Neumann models. The surface energy of fresh CVD graphene grown on a copper substrate (G/Cu) immediately after synthesis was determined to be 62.2 ± 3.1 mJ/m(2) (Fowkes), 53.0 ± 4.3 mJ/m(2) (Owens-Wendt) and 63.8 ± 2.0 mJ/m(2) (Neumann), which decreased to 45.6 ± 3.9, 37.5 ± 2.3, and 57.4 ± 2.1 mJ/m(2), respectively, after 24 h of air exposure. The ellipsometry characterization indicates that the surface energy of G/Cu is affected by airborne hydrocarbon contamination. G/Cu exhibits the highest surface energy immediately after synthesis, and the surface energy decreases after airborne contamination occurs. The root cause of intrinsically mild polarity of G/Cu surface is discussed.

Understanding the intrinsic water wettability of graphite

“…53-65° and it adsorbs airborne hydrocarbons in the ambient air to minimize surface energy, i.e., appear more hydrophobic. 76,230,241 Similar results were also reported for monolayer graphene on copper and multilayer graphene on nickel 75,77 and the surface energy and wettability of freshly synthesized graphene on copper was found to be dependent upon exposure time to ambient air. 75 Lai et al attributed the change in graphene wettability to adsorption of both water molecules and hydrocarbons 63 and Nioradze et al demonstrated that HOPG electroactivity is significantly affected by organic impurities in water and air.…”

“…76,230,241 Similar results were also reported for monolayer graphene on copper and multilayer graphene on nickel 75,77 and the surface energy and wettability of freshly synthesized graphene on copper was found to be dependent upon exposure time to ambient air. 75 Lai et al attributed the change in graphene wettability to adsorption of both water molecules and hydrocarbons 63 and Nioradze et al demonstrated that HOPG electroactivity is significantly affected by organic impurities in water and air. 59,62 Boinovich et al also showed that hydrocarbon contaminants spontaneously adsorb onto boron nitride nanotubes (BNNTs) and render the BNNTs to be hydrophobic, suggesting that other 2D materials are susceptible to spontaneous hydrocarbon contamination.…”

“…It is important to note that all experiments conducted by myself and my co-workers were taken on samples that were purchased new and once the sample got substantially thin it was replaced and no longer used for experiments. 62,70,[75][76][77] ZYA is the highest quality of HOPG and exfoliates nearly perfectly. Visually, there were no flakes or exfoliation-induced defects noticeable and all experimental testing was performed only on the visually pristine basal surface.…”

“…71,235 This mechanism is described in Section 2.2 (page 12) and in our previous work on graphene and HOPG. [75][76][77] Mangolini et al used near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and XPS to investigate the thickness and chemical nature of the adsorbed contamination layer on diamond and amorphous carbon. They reported that the contaminant layer has a thickness of 0.6 ± 0.2 nm and consists of 19 ± 3% sp 2 carbon.…”

Anhydride-based chemistry on graphene for advanced polymeric materials

“…Graphene is classied as a hydrophobic material and has demonstrated water-repulsion properties in hydrophilic polymers. 27 Despite the fact that the contact angle of graphene surfaces has been shown to be time dependent, 28,29 in our case the use of water contact angle (WCA) gives a clear estimation of the changes in graphene wettability aer functionalization with succinic anhydride (ESI, Fig. S1 †).…”