Molecular simulation study of triangle-well fluids confined in slit pores
TL;DR: In this paper, the effect of individual factors influencing the properties of confined fluids such as fluid-fluid interactions, pore size and pore wall interaction were obtained using simulations as it is difficult to experimentally determine the same.
Abstract: Grand canonical Monte Carlo simulations are used to study the behaviour of triangle-well (TW) fluids with variable well widths confined inside slit pores. The effect of individual factors influencing the properties of confined fluids such as fluid–fluid interactions, pore size and pore wall–fluid interactions are obtained using simulations as it is difficult to experimentally determine the same. An interesting observation of this study is that inside the narrow pore of slit height h* = 5 at the high-pressure condition of P* = 0.8, for the TW fluid with long-range attraction or for the fluid at a low temperature for even a short-range attraction, the density profiles show layering such that there is a sticking tendency of the particles at centre, while there is a depletion of particles near the wall (as the layers at the centre have higher density peak heights than near the walls).
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TL;DR: In this article, the authors used the Barker-Henderson perturbation theory with the macroscopic compressibility approximation (BH-MCA) of monomer fluids combined to a simple, analytic expression of the hard-sphere radial distribution function (RDF) derived by Sun.
9 citations
TL;DR: It was observed that this potential does not follow the principle of corresponding states as reported for other interaction potentials and the reduction of the dimensionality makes the phase diagram to shrink.
Abstract: With the aim of providing complementary data of the thermodynamics properties of the triangular well potential, the vapor/liquid phase diagrams for such potential with different interaction ranges were calculated in two dimensions by Monte Carlo and molecular dynamics simulations; also, the vapor/liquid interfacial tension was calculated. As reported for other interaction potentials, it was observed that the reduction of the dimensionality makes the phase diagram to shrink. Finally, with the aid of reported data for the same potential in three dimensions, it was observed that this potential does not follow the principle of corresponding states.
6 citations
TL;DR: In this article, an analytical expression for the Helmholtz free energy of particles interacting via the triangular-well pair potential (TW), in the Barker-Henderson framework, was developed.
5 citations
TL;DR: In this article, the authors used GCMC simulations to predict the CO2 adsorption capacities in carbon slit pores of height 20, 31.6, 63.2, 94.85 and 126.5 A at 673.15 and 873.5 K over a pressure range of 500-4000 kPa, which corresponds to steam reforming of the methane process.
Abstract: This work contributes to the estimation of new and complementary density data for carbon dioxide (CO2) confined in carbon slit pores at different conditions. Grand canonical Monte Carlo (GCMC) simulations were employed to predict the CO2 adsorption capacities in carbon slit pores of height 20, 31.6, 63.2, 94.85 and 126.5 A at 673.15 and 873.15 K over a pressure range of 500–4000 kPa, which corresponds to steam reforming of methane process. The bulk densities of CO2 at these temperature and pressure conditions have been estimated via isothermal–isobaric ensemble MC simulations using the Elementary Physical Model. The predicted density shows an excellent agreement with the experimental data. The adsorption capacities of CO2 in all the aforementioned pores at 673.15 and 873.15 K over the pressure range of 500–4000 kPa have also been estimated in the presence of wall–fluid interactions, in addition to the fluid–fluid interactions. The study on the thermodynamic phase behaviour of confined CO2 in the presence of wall–fluid interactions showed the existence of vapour–liquid equilibria at high temperature and pressure conditions.
2 citations
Journal Article•
TL;DR: This paper reinterprets the well known Steele 10-4-3 potential for a gas molecule interacting with a planar surface, and uses the resultant scheme to derive new potentials for cylindrical and spherical pore geometries, yielding a family of Steele-like potentials that all satisfy the correct planar limit.
Abstract: Simplified fluid-substrate interaction models derived from the Lennard-Jones potential are widely used in the simulation of gas physisorption phenomena. In this paper, we reinterpret the well known Steele 10-4-3 potential for a gas molecule interacting with a planar surface, and use the resultant scheme to derive new potentials for cylindrical and spherical pore geometries. These new potentials correctly recover the Steele result in the limit of infinite pore radius, a useful improvement over existing models. We demonstrate the new cylindrical Steele 10-4-3 potential in calculations of argon adsorption via fluid density functional theory. This potential yields markedly different adsorption behavior than existing cylindrical potentials, which follow from small but significant differences in both the strength and the shape of the fluid-surface interaction. These differences cannot be fully reconciled simply by reparameterizing (scaling) the existing models; the new potential is more realistic in design, and is especially to be preferred in studies where comparison with planar substrates is made. Finally, we discuss extensions of this approach to more complicated pore geometries, yielding a family of Steele-like potentials that all satisfy the correct planar limit.
2 citations
References
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Book•
01 Jan 2001
TL;DR: In this paper, the physics behind molecular simulation for materials science is explained, and the implementation of simulation methods is illustrated in pseudocodes and their practical use in the case studies used in the text.
Abstract: From the Publisher:
This book explains the physics behind the "recipes" of molecular simulation for materials science. Computer simulators are continuously confronted with questions concerning the choice of a particular technique for a given application. Since a wide variety of computational tools exists, the choice of technique requires a good understanding of the basic principles. More importantly, such understanding may greatly improve the efficiency of a simulation program. The implementation of simulation methods is illustrated in pseudocodes and their practical use in the case studies used in the text. Examples are included that highlight current applications, and the codes of the case studies are available on the World Wide Web. No prior knowledge of computer simulation is assumed.
6,901 citations
Book•
01 Jan 1949
TL;DR: In this article, the second law of thermodynamics is used to describe the properties of pure fluids and their properties in the context of flow process analysis, and a discussion of the application of thermodynamic analysis of processes can be found.
Abstract: Preface 1 Introduction 2 The First Law and Other Basic Concepts 3 Volumetric Properties of Pure Fluids 4 Heat Effects 5 The Second Law of Thermodynamics 6 Thermodynamic Properties of Fluids 7 Applications of Thermodynamics to Flow Processes 8 Production of Power from Heat 9 Refrigeration and Liquefaction 10 Vapor/Liquid Equilbrium: Introduction 11 Solution Thermodynamics: Theory 12 Solution Thermodynamics: Applications 13 Chemical-Reaction Equilibria 14 Topics in Phase Equilibria 15 Thermodynamic Analysis of Processes 16 Introduciton to Molecular Thermodynamics Appendixes A Conversion Factors and Values of the Gas Constant B Properties of Pure Species C Heat Capacities and Property Changes of Formation D Representative Computer Programs E The Lee/Kesler Generalized-Correlation Tables F Steam Tables G Thermodynamic Diagrams H UNIFAC Method I Newton's Method Author Index Subject Index
3,684 citations
01 Jan 2002
921 citations
"Molecular simulation study of trian..." refers background in this paper
...The external pressure is the pressure of the bulk phase TW fluid reservoir in contact with the pore and is referred to hereafter as the ‘pressure’ [12,32,73]....
[...]
...Frenkel and Smit [73] have also noted that the GC ensemble is the ‘natural’ ensemble for studying adsorption....
[...]
TL;DR: It is shown that the type of hysteresis loop formed by adsorption/desorption isotherms is determined by different mechanisms of condensation and evaporation and depends upon the shape and size of pores, and a novel hybrid nonlocal density functional theory (NLDFT) method is elaborate for calculations of pore size distributions from advertisers in the entire range of micro- and mesopores.
Abstract: We report results of nitrogen and argon adsorption experiments performed at 77.4 and 87.3 K on novel micro/mesoporous silica materials with morphologically different networks of mesopores embedded into microporous matrixes: SE3030 silica with worm-like cylindrical channels of mode diameter of approximately 95 angstroms, KLE silica with cage-like spheroidal pores of ca. 140 angstroms, KLE/IL silica with spheroidal pores of approximately 140 angstroms connected by cylindrical channels of approximately 26 angstroms, and, also for a comparison, on Vycor glass with a disordered network of pores of mode diameter of approximately 70 angstroms. We show that the type of hysteresis loop formed by adsorption/desorption isotherms is determined by different mechanisms of condensation and evaporation and depends upon the shape and size of pores. We demonstrate that adsorption experiments performed with different adsorptives allow for detecting and separating the effects of pore blocking/percolation and cavitation in the course of evaporation. The results confirm that cavitation-controlled evaporation occurs in ink-bottle pores with the neck size smaller than a certain critical value. In this case, the pressure of evaporation does not depend upon the neck size. In pores with larger necks, percolation-controlled evaporation occurs, as observed for nitrogen (at 77.4 K) and argon (at 87.3 K) on porous Vycor glass. We elaborate a novel hybrid nonlocal density functional theory (NLDFT) method for calculations of pore size distributions from adsorption isotherms in the entire range of micro- and mesopores. The NLDFT method, applied to the adsorption branch of the isotherm, takes into account the effect of delayed capillary condensation in pores of different geometries. The pore size data obtained by the NLDFT method for SE3030, KLE, and KLE/IL silicas agree with the data of SANS/SAXS techniques.
509 citations
TL;DR: In this paper, the phase equilibria of a simple fluid confined by two adsorbing walls have been investigated as a function of wall separation H and chemical potential μ for temperature T corresponding to both partial and complete wetting situations.
Abstract: By means of a density functional approach the phase equilibria of a simple fluid confined by two adsorbing walls have been investigated as a function of wall separation H and chemical potential μ for temperature T corresponding to both partial and complete wetting situations. For large values of H and small undersaturations Δμ ≡ μsat−μ, we recover the macroscopic formulas for the undersaturation at which a first‐ order phase transition (capillary condensation) from dilute ‘‘gas’’ to a dense ‘‘liquid’’ occurs in a single, infinitely long slit. For smaller H we compute the lines of coexistence between gas and liquid in the (Δμ, 1/H) plane at fixed values of T. The adsorption Γ(Δμ), at fixed T and H, is characterized by a loop. At the first order transition Γ jumps discontinuously by a finite amount; however metastable states exist and these could give rise to hysteresis of the adsorption isotherms obtained for the single slit. The loop disappears at a capillary critical point (Δμc, 1/Hc) at each T. For H
464 citations