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Journal ArticleDOI

Effect of the fluid-wall interaction on freezing of confined fluids: Toward the development of a global phase diagram

14 Jun 2000-Journal of Chemical Physics (American Institute of PhysicsAIP)-Vol. 112, Iss: 24, pp 11048-11057
TL;DR: In this article, the effect of the fluid-wall interaction energy on the shift of the freezing temperature and on the fluid structure is considered, using a novel approach to calculate the free energy surface based on Landau theory and order parameter formulation.
Abstract: We report molecular simulation studies of the freezing behavior of fluids in nano-porous media. The effect of confinement is to induce spatial constraints as well as energetic heterogeneity on the confined fluid, thereby altering the bulk phase behavior drastically. We consider the effect of the fluid-wall interaction energy on the shift of the freezing temperature and on the fluid structure, using a novel approach to calculate the free energy surface based on Landau theory and order parameter formulation. Corresponding states theory is then used to map out the global freezing behavior of a Lennard-Jones (LJ) fluid in model slit-shaped pores of varying fluid-wall interaction strengths. Using LJ parameters fitted to thermophysical property behavior, we predict the qualitative freezing behavior for a variety of fluids and nano-porous materials, based on a global freezing diagram. We have attempted to verify these predictions by comparing with experimental data for several systems, and show that in these cases, the experimental observations and the predictions are in agreement.

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Citations
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Journal ArticleDOI
TL;DR: The STMD method is demonstrated to be a robust way for probing the phase transitions of nanoconfined fluids systematically, enabling the future examination of the phase transition behavior of more complex fluids.
Abstract: The fluid-solid phase transition behavior of nano-confined Lennard-Jones fluids as a function of temperature and degree of nanoconfinement has been studied via statistical temperature molecular dynamics (STMD). The STMD method allows the direct calculation of the density of states and thus the heat capacity with high efficiency. The fluids are simulated between parallel solid surfaces with varying pore sizes, wall-fluid interaction energies, and registry of the walls. The fluid-solid phase transition behavior has been characterized through determination of the heat capacity. The results show that for pores of ideal-spacing, the order-disorder transition temperature (T(ODT)) is reduced as the pore size increases until values consistent with that seen in a bulk system. Also, as the interaction between the wall and fluid is reduced, T(ODT) is reduced due to weak constraints from the wall. However, for non-ideal spacing pores, quite different behavior is obtained, e.g., generally T(ODT) are largely reduced, and T(ODT) is decreased as the wall constraint becomes larger. For unaligned walls (i.e., whose lattices are not in registry), the fluid-solid transition is also detected as T is reduced, indicating non-ideality in orientation of the walls does not impact the formation of a solid, but results in a slight change in T(ODT) compared to the perfectly aligned systems. The STMD method is demonstrated to be a robust way for probing the phase transitions of nanoconfined fluids systematically, enabling the future examination of the phase transition behavior of more complex fluids.

8 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the density distribution, fluid structure and solvation forces for fluids confined in Janus slit-shaped pores using grand canonical Monte Carlo simulations and found that the presence of one moderately attractive surface in the asymmetric pore is sufficient to disrupt the formation of frozen phases observed in the symmetric case.
Abstract: Density distribution, fluid structure and solvation forces for fluids confined in Janus slit-shaped pores are investigated using grand canonical Monte Carlo simulations. By varying the degree of asymmetry between the two smooth surfaces that make up the slit pores, a wide variety of adsorption situations are observed. The presence of one moderately attractive surface in the asymmetric pore is sufficient to disrupt the formation of frozen phases observed in the symmetric case. In the extreme case of asymmetry in which one wall is repulsive, the pore fluid can consist of a frozen contact layer at the attractive surface for smaller surface separations (H) or a frozen contact layer with liquid-like and gas-like regions as the pore width is increased. The superposition approximation, wherein the solvation pressure and number density in the asymmetric pores can be obtained from the results on symmetric pores, is found to be accurate for H > 4 sigma(ff), where sigma(ff) is the Lennard-Jones fluid diameter and within 10% accuracy for smaller surface separations. Our study has implications in controlling stick slip and overcoming static friction `stiction' in micro and nanofluidic devices.

8 citations


Cites background from "Effect of the fluid-wall interactio..."

  • ...[30], an elevation in freezing temperature for fluids confined in slit-shaped pores was found to occur when the dimensionless parameter, a*=2p 1⁄4 rw1fws2 fw (Equation (2)), was greater than 1....

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  • ...[30], which is based on a principle of corresponding states, was developed for pore widths ....

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Dissertation
01 Jan 2010
TL;DR: This chapter is intended to be a prologue to a chapter on “How to Train Your Dragon”, which explores the themes of self-confidence and self-esteem and the importance of positive emotions.
Abstract: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviii Chapter

8 citations


Cites background from "Effect of the fluid-wall interactio..."

  • ...Tracking structural transitions is important for a wide variety of applications, including elucidating thermodynamic transitions [57, 348, 349, 350, 351] and assembly pathways [29, 352, 353, 268]....

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  • ..., the spatial ordering within a single plane in a confined fluid [350,351] or the crystalline arrangement of cylindrical domain [298, 314]) and “q"” is used when we wish to describe the 3d ordering (e....

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Journal ArticleDOI
TL;DR: In this article, a molecular simulation examination of the fundamentals of the pore-load measurement technique is presented, and the results are compared with the expected mechanical response of the solid.
Abstract: Liquid adsorption in nanoporous materials induces their deformation due to strong capillary and disjoining forces. The linear relationship between the liquid pressure and the solid strain (pore-load modulus) provides an experimental technique to determine the mechanical properties of nanosized solids. Puzzling experimental results have often been reported, leading to a severe reconsideration of the mechanical properties of the thin walls, the introduction of surface stresses, and the suggestion of a mutual influence of fluid adsorption and matrix deformation. This work presents a molecular simulation examination of the fundamentals of the pore-load measurement technique. The pore-load protocol is reproduced as in experiments by measuring the solid deformation in the presence of the liquid (“numerical experiment”), and the result is compared with the expected mechanical response of the solid. Focusing on a single nanoplatelet mimicking silicon stiffness, we show that the pore-load protocol is valid as long...

7 citations

Journal ArticleDOI
TL;DR: In this paper, it is shown that the glass transition temperature T g is depressed or increased depending on the nature of the interactions at the interface, and that these effects can be interpreted in the framework of the free volume model.
Abstract: In glass-forming materials confined in films or pores of small dimension, the glass transition temperature T g is depressed or increased depending on the nature of the interactions at the interface. It is shown that these effects, observed in polymers and simple liquids, can be interpreted in the framework of the free volume model. Similar effects of confinement on the glass and melting transitions are stressed; this permits prediction of the variations of the cooperative molecular motions α with temperature.

7 citations


Cites background from "Effect of the fluid-wall interactio..."

  • ...The crystallization of organic compounds, minerals, polymers, and metals in porous glass and other confined systems has been studied for a long time, see, for example, the recent review of Gelb et al.[20] As recalled in the introduction, the effect of a decrease of the melting temperatures Tm, with the confined size is well known; in addition only a few cases of increase have been reported....

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  • ...This effect has been explained by simulation works.([20]) Recently, Wautelet([26]) has proposed a phenomenological model, based on the surface phonon interaction theory, to estimate the variation of Tm with 1=‘c....

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  • ...It must be noted that similar increases or decreases of the melting temperature Tm are observed in organic, mineral, and metallic materials, which are crystallized in confined geometry.([20]) By various spectroscopy methods, the relaxation map of the GFM can be obtained in a large domain of frequency, 10(6) < n < 10 (2)....

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  • ...The crystallization of organic compounds, minerals, polymers, and metals in porous glass and other confined systems has been studied for a long time, see, for example, the recent review of Gelb et al.([20]) As recalled in the introduction, the effect of a decrease of the melting temperatures Tm, with the confined size is well known; in addition only a few cases of increase have been reported....

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References
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Book
01 Jan 1954
TL;DR: Molecular theory of gases and liquids as mentioned in this paper, molecular theory of gas and liquids, Molecular theory of liquid and gas, molecular theories of gases, and liquid theory of liquids, مرکز
Abstract: Molecular theory of gases and liquids , Molecular theory of gases and liquids , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

11,807 citations

Book
01 Jan 1995
TL;DR: In this article, the authors present a generalization of the renormalization group of mean field theories, critical phenomena, and topological defects, including walls, kinks and solitons.
Abstract: Preface 1. Overview 2. Structure and scattering 3. Thermodynamics and statistical mechanics 4. Mean-field theory 5. Field theories, critical phenomena, and the renormalization group 6. Generalized elasticity 7. Dynamics: correlation and response 8. Hydrodynamics 9. Topological defects 10. Walls, kinks and solitons Glossary Index.

3,223 citations

Journal ArticleDOI
TL;DR: In this paper, the potential energy of a gas atom interacting with a solid having a surface made up of single type of exposed lattice plane can be expressed as a Fourier series in the position variables in the plane parallel to the surface.

1,379 citations

Journal ArticleDOI
TL;DR: In this paper, the free energy of a Lennard-Jones fluid in the liquid-vapour coexistence region was estimated by relating it to that of the inverse-twelve (soft sphere) fluid, which itself shows no condensation.

1,179 citations