Calculation of a solid/liquid surface tension: A methodological study

Abstract

The surface tension of a model solid/liquid interface constituted of a graphene sheet surrounded by liquid methane has been computed using molecular dynamics in the Kirkwood-Buff formalism. We show that contrary to the fluid/fluid case, the solid/liquid case can lead to different structurations of the first fluid layer, leading to significantly different values of surface tension. Therefore we present a statistical approach that consists in running a series of molecular simulations of similar systems with different initial conditions, leading to a distribution of surface tensions from which an average value and uncertainty can be extracted. Our results suggest that these distributions converge as the system size increases. Besides we show that surface tension is not particularly sensitive to the choice of the potential energy cutoff and that long-range corrections can be neglected contrary to what we observed in the liquid/vapour interfaces. We have not observed the previously reported commensurability effect.

Surface morphology effects on clathrate hydrate wettability

“…Simulated Interfacial Tensions. Molecular modelling has been shown promising in investigations of interfacial forces at solid-liquid interfaces and in fact, it has been widely employed to estimate surface free energies [51][52][53][54]. In recent years, multiple approaches have been proposed to quantify solid-liquid interfacial free energy.…”

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

“…For the calculation of the solid-liquid interfacial tension, the impact of some of the factors mentioned above is still unknown. Concerning the long-range corrections to the interfacial tension of the graphene-methane interface modeled only with Lennard-Jones interactions, we have established that these tail corrections were negligible with respect to the intrinsic contribution even with a small cutoff value (r c = 12Å) [20,21]. Does it mean that the choice of the cutoff radius will have no impact on the calculation of the intrinsic part of the interfacial tension of solid-liquid interfaces for truncated potentials ?…”

“…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].…”

Associated molecular liquids at the graphene monolayer interface

“…The water molecules at the interfacial region show stronger hydrogen bonds 49,50 and different orientations with respect to bulk conditions. Additionally, molecules that interact with the solid in the first adsorption layer can be subjected to tangential pressures of the order of hundreds of MPa 31,37 whereas negative tangential pressure of ten MPa occur in the liquidvapor interfaces for the same liquid molecules. These interfacial tensions find their molecular origin in a surface effect leading to a compression in the direction parallel to the surface due to the tangential pressure component.…”

“…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 .…”