Computational Simulations of Nanoconfined Argon Film through Adsorption–Desorption in a Uniform Slit Pore

Rong-Guang Xu,Yuan Xiang,Qi Rao,Motong Bian,Yongsheng Leng

doi:10.3390/coatings11020177

Rong-Guang Xu, Yuan Xiang + Show 3 more

Open Access

https://doi.org/10.3390/coatings11020177

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Journal: Coatings	Publication Date: Feb 2, 2021
Citations: 2	License type: CC BY 4.0

Affiliation: George Washington University, Idaho National Laboratory

Abstract

We performed hybrid grand canonical Monte Carlo/molecular dynamics (GCMC/MD) simulations to investigate the adsorption-desorption isotherms of argon molecules confined between commensurate and incommensurate contacts in nanoscale thickness. The recently proposed mid-density scheme was applied to the obtained hysteresis loops to produce a realistic equilibrium phase of nanoconfined fluids. The appropriate chemical potentials can be determined if the equilibrium structures predicted by GCMC/MD simulations are consistent with those observed in previously developed liquid-vapor molecular dynamics (LVMD) simulations. With the chemical potential as input, the equilibrium structures obtained by GCMC/MD simulations can be used as reasonable initial configurations for future metadynamics free energy calculations.

Highlights

The structure and thermodynamic state of a liquid film confined between two solid surfaces in nanoscale thickness and its mechanical response to external loading are very important topics in surface science [1], which has attracted considerable interests and research efforts for decades in many surface force experiments (mainly in surface force apparatus (SFA) or surface force balance (SFB) measurements) [2,3,4,5] and molecular simulations [6,7]
The main features of the liquid-vapor molecular dynamics (LVMD) simulation can be summarized in three aspects: First, it enables the squeeze-out of the confined fluid during normal compression due to the extended side walls along the squeeze-out direction
Our previous LVMD simulations show that the critical layer number, nc, at which

Summary

Introduction

The structure and thermodynamic state of a liquid film confined between two solid surfaces in nanoscale thickness and its mechanical response to external loading are very important topics in surface science [1], which has attracted considerable interests and research efforts for decades in many surface force experiments (mainly in surface force apparatus (SFA) or surface force balance (SFB) measurements) [2,3,4,5] and molecular simulations [6,7]. We need to first understand the actual equilibrium structure of a nanoconfined liquid film that should correspond to a lowest free energy state These equilibrium states may not be fully explored by the SFA/B mechanical driving system due to its nonequilibrium nature of driven dynamics during unstable transitions. A liquid-vapor molecular dynamics (LVMD) ensemble was used to investigate the force oscillation, phase transition, and shearing behaviors of liquid films confined between two solid walls [12,13,14,15,16]. In our previous study [14], grand canonical Monte Carlo (GCMC) and LVMD simulations were carried out to study the squeezing and phase transition of simple liquid argon confined between two commensurate solid surfaces.

Simulation Models and Methods

Commensurate Contact Simulations

Layer 5 Layer