Gibbs Ensemble Monte Carlo Simulation of Fluids in Confinement: Relation between the Differential and Integral Pressures.

Máté Erdős,Thijs J H Vlugt,Olav Galteland,Dick Bedeaux,Signe Kjelstrup,Othonas A Moultos

doi:10.3390/nano10020293

Abstract

The accurate description of the behavior of fluids in nanoporous materials is of great importance for numerous industrial applications. Recently, a new approach was reported to calculate the pressure of nanoconfined fluids. In this approach, two different pressures are defined to take into account the smallness of the system: the so-called differential and the integral pressures. Here, the effect of several factors contributing to the confinement of fluids in nanopores are investigated using the definitions of the differential and integral pressures. Monte Carlo (MC) simulations are performed in a variation of the Gibbs ensemble to study the effect of the pore geometry, fluid-wall interactions, and differential pressure of the bulk fluid phase. It is shown that the differential and integral pressure are different for small pores and become equal as the pore size increases. The ratio of the driving forces for mass transport in the bulk and in the confined fluid is also studied. It is found that, for small pore sizes (i.e., <), the ratio of the two driving forces considerably deviates from 1.

Highlights

The widespread application of nanoporous materials in several fields, such as chromatography, membrane separation, catalysis, etc., has lead to a growing interest in the accurate description of the thermodynamic behavior of fluids confined in nanopores [1,2,3,4,5,6]
The pressure of a nanoconfined fluid is one of the most important thermodynamic properties which is needed for an accurate description of the flow rate, diffusion coefficient, and the swelling of the nanoporous material [7,8,9,10]
Since the aim of this study is to show the difference between the differential and integral pressures and not to simulate some specific adsorption system, only two types of interaction potentials are considered for the interaction of fluid particles with the wall in Simulation Box 2

Summary

Introduction

The widespread application of nanoporous materials in several fields, such as chromatography, membrane separation, catalysis, etc., has lead to a growing interest in the accurate description of the thermodynamic behavior of fluids confined in nanopores [1,2,3,4,5,6]. The pressure of a nanoconfined fluid is one of the most important thermodynamic properties which is needed for an accurate description of the flow rate, diffusion coefficient, and the swelling of the nanoporous material [7,8,9,10]. Various approaches for calculating the pressure of a fluid in a nanopore have been proposed [1,11,12,13]. Several methods were reported using different simulation techniques i.e., classical density functional theory [17,18], equation of state modeling [19], etc., to model the behavior of fluids in confinement

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Conclusion