Energy Effects on the Structure and Thermodynamic Properties of Nanoconfined Fluids (A Density Functional Theory Study)

Keshavarzi, Ezat; Kamalvand, Mohammad

doi:10.1021/jp808466p

Cited by 20 publications

(13 citation statements)

References 23 publications

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“…It is well known that thermodynamic properties of fluids significantly change when the fluid phases become confined [1,2]. Given the importance of porous media for applications in for example fuel cells [3], batteries [4], and membranes for drinking water production [5][6][7], it is essential to understand how properties change upon confinement.…”

Section: Introductionmentioning

confidence: 99%

Two-Phase Equilibrium Conditions in Nanopores

et al. 2020

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It is known that thermodynamic properties of a system change upon confinement. To know how, is important for modelling of porous media. We propose to use Hill’s systematic thermodynamic analysis of confined systems to describe two-phase equilibrium in a nanopore. The integral pressure, as defined by the compression energy of a small volume, is then central. We show that the integral pressure is constant along a slit pore with a liquid and vapor in equilibrium, when Young and Young–Laplace’s laws apply. The integral pressure of a bulk fluid in a slit pore at mechanical equilibrium can be understood as the average tangential pressure inside the pore. The pressure at mechanical equilibrium, now named differential pressure, is the average of the trace of the mechanical pressure tensor divided by three as before. Using molecular dynamics simulations, we computed the integral and differential pressures, p ^ and p, respectively, analysing the data with a growing-core methodology. The value of the bulk pressure was confirmed by Gibbs ensemble Monte Carlo simulations. The pressure difference times the volume, V, is the subdivision potential of Hill, ( p − p ^ ) V = ϵ . The combined simulation results confirm that the integral pressure is constant along the pore, and that ϵ / V scales with the inverse pore width. This scaling law will be useful for prediction of thermodynamic properties of confined systems in more complicated geometries.

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Section: Introductionmentioning

confidence: 99%

Two-Phase Equilibrium Conditions in Nanopores

et al. 2020

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“…The MFMT for the repulsive contribution has been demonstrated to perform very well in describing the properties of inhomogeneous fluids on planar solid surfaces . The ability of the improved DFT for predicting a large variety of phase transitions of confined fluids has also been well tested. , Very recently, the thermodynamic consistency of the above version has been examined to be reliable despite some approximations involved . To investigate the effects of gas enrichment and liquid depletion, the density profiles of different dissolved gases and the liquid in the vicinity of the hydrophobic wall are calculated.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Study of Dissolved Gas at a Hydrophobic Interface

Zhou

Zhong

2012

J. Phys. Chem. C

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In this work, the classic density functional approach is applied to describe the interfacial structure and properties of the dissolved gas and liquid in the presence of a hydrophobic wall. In the theoretical approach, the modified fundamental measure theory is adopted for the hard-sphere reference term, and the weighted density approximation is applied for the attractive term. The vapor−liquid phase coexistence curve and the interfacial tensions of Lennard-Jones binary mixtures are first calculated. The results are in good agreement with the corresponding simulation data, indicating that the approach is suitable to study the inhomogeneous properties of fluid mixtures. The density profiles of dissolved gas and liquid in the vicinity of the hydrophobic surface are then calculated. It is shown that distinctive gas enrichment and liquid depletion occur in the interfacial region, and the effects can be reinforced as the dispersion potential and molecule diameter of the gas increase. Based on the supersaturation induced by the gas enrichment and liquid depletion, the free energy barriers of bubble nucleation on the solid wall are approximately estimated for different gases to analyze the probability of spontaneous bubble nucleation near the hydrophobic surface.

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“…In fact, for confined fluids, introduction of the hard walls can essentially change the system's energy compared to the bulk through cutting off of some intermolecular interactions. 18 This effect of walls on the moleculeÀmolecule interactions for fluids with long-range forces may favor the adsorption of species with weaker attractive intermolecular interactions into the nanopore in comparison to other components in the mixtures. In our studied systems in Figure 2 the population distribution of molecules inside the nanoslit is determined by the competition between two factors, bulk concentration, and the energy effect.…”

Section: Resultsmentioning

confidence: 99%

“…Among different theoretical methods for studying inhomogeneous systems we have used density functional theory (DFT) whose ability for predicting a large variety of phase transitions of confined fluids has been proved. 17,18 Modified fundamental measure theory 19,20 (MFMT) is one of the most successful versions of DFT that provides improved structure for hard sphere fluids near the walls 21 and in confined geometries. 18,22 The weight functions in this theory are characteristics of each type of molecules making it applicable to mixtures.…”

Section: Introductionmentioning

confidence: 99%

“…Among different theoretical methods for studying inhomogeneous systems we have used density functional theory (DFT) whose ability for predicting a large variety of phase transitions of confined fluids has been proved. , Modified fundamental measure theory , (MFMT) is one of the most successful versions of DFT that provides improved structure for hard sphere fluids near the walls and in confined geometries. , The weight functions in this theory are characteristics of each type of molecules making it applicable to mixtures. We have incorporated the excess Helmholtz free energy functional in terms of MFMT for the hard sphere repulsion and mean field approximation for long-range attractions to construct the Helmholtz free energy functional of the mixtures.…”

Section: Introductionmentioning

confidence: 99%

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Population Inversion of Binary Lennard-Jones Mixtures in Nanoslit Pores (A Density Functional Theory Study)

Taghizadeh¹,

Keshavarzi²

2011

J. Phys. Chem. B

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The aim of this work is to investigate the population inversion of binary asymmetric Lennard-Jones mixtures inside nanoslit pores due to confinement effects for both vapor and liquid phases. For this purpose we have used mean field fundamental measure theory, and the effect of different parameters such as interaction strength and size ratios of the components, confinement size, and thermodynamic state on the population distribution of molecules have been studied. It has been shown that in the case of bulk liquid mixtures, increasing the role of confinement effects can lead to preferential adsorption of the component with larger size and weaker intermolecular interactions into the nanopore in spite of its minority in the bulk which is referred as population inversion. This population inversion phenomenon is terminated by a sudden condensation which, interestingly, involves a simultaneous adsorption and desorption for more and less bulk concentrated species, respectively. We have demonstrated that this condensation phenomenon shifts to higher bulk densities with increasing the role of confinement effects such that in some cases population inversion is observable for the whole range of densities. In consideration of the conditions in which vapor Lennard-Jones mixtures undergo capillary condensation, the population distribution of components in the vapor- and liquidlike phases was studied. It has been shown that variation of parameters such as interaction strength and size ratios, temperature, and confinement size can lead to conditions in which capillary condensation is accompanying with a population inversion phenomenon. In these cases, whereas the composition of vaporlike phases is the same as bulk fluid, liquidlike phases are richer in the component with less bulk concentration.

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Energy Effects on the Structure and Thermodynamic Properties of Nanoconfined Fluids (A Density Functional Theory Study)

Cited by 20 publications

References 23 publications

Two-Phase Equilibrium Conditions in Nanopores

Two-Phase Equilibrium Conditions in Nanopores

Theoretical Study of Dissolved Gas at a Hydrophobic Interface

Population Inversion of Binary Lennard-Jones Mixtures in Nanoslit Pores (A Density Functional Theory Study)

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