Test-area surface tension calculation of the graphene-methane interface: Fluctuations and commensurability

Abstract

The surface tension (γ) of methane on a graphene monolayer is calculated by using the test-area approach. By using a united atom model to describe methane molecules, strong fluctuations of surface tension as a function of the surface area of the graphene are evidenced. In contrast with the liquid-vapor interfaces, the use of a larger cutoff does not fully erase the fluctuations in the surface tension. Counterintuitively, the description of methane and graphene from the Optimized Potentials for Liquid Simulations all-atom model and a flexible model, respectively, led to a lessening in the surface tension fluctuations. This result suggests that the origin of fluctuations in γ is due to a model-effect rather than size-effects. We show that the molecular origin of these fluctuations is the result of a commensurable organization between both graphene and methane. This commensurable structure can be avoided by describing methane and graphene from a flexible force field. Although differences in γ with respect to the model have been often reported, it is the first time that the model drastically affects the physics of a system.

Computational Assessment of Water Desalination Performance of Multi‐Walled Carbon Nanotubes

“…[ 4–6,8,11,44–47 ] Furthermore, recent works have highlighted that the rigid force field of graphitic frameworks was capable to quantitatively reproduce the interfacial properties, which suggests that the flexibility of CNT does not impact the interfacial transport. [ 48,49 ] Nevertheless, to evaluate the impact of the flexibility the Tersoff potential was considered to model a flexible CNT1. [ 39 ] From the Tersoff model a water permeability of 256.8 molecules per ns was found, which is close to the permeability obtained with the rigid CNT1 (229.2 molecules per ns).…”

“…Recently, it has been shown that this force field provided a good agreement between the experimental and calculated surface tensions between water and methane and graphene. [ 48,49 ] The parameters of the various potentials are given in Table S3, Supporting Information). The pressure exerted on each wall corresponds to where A is the surface area of the wall and N p the number of carbon atoms in the wall.…”

Associated molecular liquids at the graphene monolayer interface

“…By considering a pristine graphene sheet, it is now possible to calculate directly the graphene-water interfacial tension by molecular simulations 31 through the stress profile. Indeed, the methodological parameters [32][33][34][35] that have impacted the calculation of the surface tension of liquid-vapor interfaces for a long time (at least 40 years) are now under control and are in the process of being controlled for the calculation of the interfacial tension of solid-liquid interfaces 31,36,37 .…”

Interfacial tension of the graphene–water solid–liquid interface: how to handle the electrostatic interactions?

“…In addition, depending of the geometry and nature of the solid surface, the calculation can become much more difficult because the internal stresses in the solid [22] has to be calculated. In the case of the graphene sheet immersed immersed in methane [20,23] and water [21], it is possible to limit the calculation of the interfacial tension to that of the stress profile provided that the graphene is considered rigid. This is a reasonable approximation based on the extremely high values of Young's modulus and strength [24].…”

“…Our previous works aimed to establish the system-size at which we no longer observe size-effects [21,23]. In this paper, we aim to investigate the effects of changing the cutoff radius on the graphene-water interfacial tensions as the calculation of the electrostatic interactions is performed with the Ewald method, Reaction Field (RF) [28] and a damped version of The Reaction Field (RFD) [29] methods.…”