What Is the Contact Angle of Water on Graphene?

Abstract

Although experimental and theoretical studies have addressed the question of the wetting properties of graphene, the actual value of the contact angle of water on an isolated graphene monolayer remains unknown. While recent experimental literature indicates that the contact angle of water on graphite is in the range 90-95°, it has been suggested that the contact angle on graphene may either be as high as 127° or moderately enhanced in comparison with graphite. With the support of classical molecular dynamics simulations using empirical force-fields, we develop an argumentation to show that the value of 127° is an unrealistic estimate and that a value of the order of 95-100° should be expected. Our study establishes a connection between the variation of the work of adhesion of water on graphene-based surfaces and the interaction potential between individual water molecules and these surfaces. We show that a variation of the contact angle from 90° on graphite to 127° on graphene would imply that both of the first two carbon layers of graphite contribute approximately the same interaction energy with water. Such a situation is incompatible with the short-range nature of the interaction between water and this substrate. We also show that the interaction potential energy between water and the graphene-based substrates is the main contribution to the work of adhesion of water with a relative magnitude that is independent of the number of graphene layers. We introduce the idea that the remaining contribution is entropic in nature and is connected to the fluctuations in the water-substrate interaction energy.

Layer Dependent Wetting in Parahexaphenyl Thin Film Growth on Graphene

“…Some groups found an impact on the wetting properties of water depending on the substrate and the Gr layer number as a result of wetting transparency [10][11][12]. Other researchers deduced, based on a thermodynamic model and molecular dynamics simulations, decreasing water contact angles for the first 3 layers of unsupported Gr [13]. In contrast to that, further groups found that the water contact angles are essentially independent from the support as well as from the number of Gr layers and are the same for highly oriented pyrolytic graphite (HOPG).…”

“…Recently, Gr has also been investigated towards the possibility to create surfaces with tunable wettability [10][11][12]. Contradictory results and interpretations of the findings triggered a discussion about Gr thickness dependent wetting properties of water [13][14][15]. An answer to the question of Gr layer dependent wetting is not only relevant for applications of interfaces between graphitic carbons and liquids -as used in electro-chemical storage devices like batteries or supercapacitors -but is also fundamental for the control of thin film growth.…”

Removal of heavy metals and pollutants by membrane adsorption techniques

“…This technology has the potential to revolutionize water filtration across the world, in particular in countries which cannot afford large scale desalination plants (Robinson 2017;Abraham et al 2017). Graphine oxide (GO) as adsorbent for the removal of heavy metals is getting more attention due to its high surface area, mechanical strength, light weight, flexibility and chemical stability (Gopalakrishnan et al 2015;Taherian et al 2013;Kyzas et al 2014) wrote a review and discussed the application of GO (particularly as magnetic particles) as an adsorbent for wastewater treatment such as heavy metals separation (mercury, cadmium, copper, chromium, arsenic) and also organics (antibiotics, dyes, i.e. Reactive black 5, etc.).…”

Water on BN doped benzene: A hard test for exchange-correlation functionals and the impact of exact exchange on weak binding

“…Particularly for complex organic systems, predicting the exact lowest energy conformation is crucial to determine the crystal structure of drugs 9,10 and the mechanisms by which proteins function. 11 One particularly interesting weakly interacting system of relevance to potential applications in clean energy, water pua) Electronic mail: angelos.michaelides@ucl.ac.uk rification, hydrogen storage, and bio-sensing, [12][13][14][15][16] is the interaction of water with layered materials. Notably interfacial water on graphene, hexagonal boron nitride (h-BN), and hybrid composites of these materials.…”

“…Indeed thanks to remarkable advances in combining boron, nitrogen, and carbon atoms in a cyclic aromatic arrangement it is now possible to create two-dimensional sheets with carefully structured regions of carbon and boron nitride. [17][18][19] Despite the growing number of studies for water on h-BN [20][21][22] and graphene 15,16,[23][24][25][26][27] there are no direct measurements of adsorption energies for the water monomer, and the theoretical adsorption energies for these systems vary significantly across different high accuracy methods. 25,[27][28][29] One can use smaller model systems for graphene 25,[29][30][31][32] and h-BN, such as benzene and the inorganic counterpart borazine (B 3 N 3 H 6 ), to help understand the interaction with water.…”