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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TL;DR: In this paper, the phase diagram of the confined mixtures are of the same type as that for the bulk mixture (eutectic), however, in the case of mixtures in carbon nanopores the solid/liquid coexistence lines are located at higher temperatures than for the Bulk mixtures, whereas they are at lower temperatures than the bulk for mixtures confined in silica pores.
Abstract: We report experimental results for the melting of eutectic mixtures confined in nanoporous matrices. Dielectric relaxation spectroscopy and differential scanning calorimetry were used to determine the solid/liquid phase diagram of C6H4Br2/CCl4 mixtures confined in controlled pore glasses (CPG) with an average pore diameter of 7.5 nm, and C6H5Br/CCl4 mixtures confined in activated carbon fibers (ACF) with a mean pore diameter of 1.4 nm. We find that the phase diagram of the confined mixtures are of the same type as that for the bulk mixture (eutectic). However, in the case of mixtures in carbon nanopores the solid/liquid coexistence lines are located at higher temperatures than for the bulk mixtures, whereas they are at lower temperatures than the bulk for mixtures confined in silica pores. These results are compared with those previously obtained for azeotropic mixtures in ACF. The results suggest that the melting temperatures, Tmp, of confined mixtures decrease relative to the bulk when the fluid–wall in...
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TL;DR: In this paper, the melting transition of bulk and confined Stockmayer fluids (μ2 = 1) was analyzed using molecular dynamic simulations, and the solid-liquid coexistence temperature was evaluated using a modified three-stage pseudo-supercritical transformation path.
Abstract: The melting transition of bulk and confined Stockmayer fluids (μ2 = 1) is analyzed using molecular dynamic simulations. The solid–liquid coexistence temperature is evaluated using a modified three-stage pseudo-supercritical transformation path. The bulk melting temperature calculated using the aforementioned method agrees well with the literature value. Melting temperatures of the Stockmayer fluid confined in Lennard-Jones (LJ) 9–3 slit pore of pore size, H, varying from 6 to 20 molecular diameters are reported. For H ≤ 12 molecular diameters, the shift in the melting temperature for the Stockmayer fluid is oscillatory in nature with the inverse of the pore size. However, for higher H the shift in melting temperature obeys the Gibbs–Thomson equation. The thermodynamic melting temperatures of the Stockmayer fluid under confinement, for variable pore sizes, are found to be usually higher than that of the bulk fluid. The structural and orientational order parameters are also presented, which suggest similari...
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TL;DR: The properties and performance of a new composite material able to form gas clathrates with hydroquinone (HQ) deposited on alumina particles exceeds that of pure HQ and HQ-silica composites developed in a previous study, opening up new opportunities for the design and use of these novel materials for gas separation.
Abstract: Organic clathrates formed by hydroquinone (HQ) and gases such as CO2 and CH4 are solid supramolecular host–guest compounds in which the gaseous guest molecules are encaged in a host framework of HQ molecules. Not only are these inclusion compounds fascinating scientific curiosities but they can also be used in practical applications such as gas separation. However, the development and future use of clathrate-based processes will largely depend on the effectiveness of the reactive materials used. These materials should enable fast and selective enclathration and have a large gas storage capacity. This article discusses the properties and performance of a new composite material able to form gas clathrates with hydroquinone (HQ) deposited on alumina particles. Apart from the general characterization of the HQ-alumina composite, one of the most remarkable observations is the unexpected formation of a guest-free clathrate structure with long-term stability (>2 years) inside the composite. Interestingly enough, in addition to a slight improvement in the enclathration kinetics of pure CO2 compared to powdered HQ, preferential capture of CO2 molecules is observed when the HQ-alumina composite is exposed to an equimolar CO2/CH4 gas mixture. In terms of gas capture selectivity toward CO2, the performance of this new composite exceeds that of pure HQ and HQ-silica composites developed in a previous study, opening up new opportunities for the design and use of these novel materials for gas separation.
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DOI•
01 Jan 2007
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Cites background from "Effect of the fluid-wall interactio..."
...There have been a large number of studies of liquids in confined pores where ordering at the interface is observed[91-95]....
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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.
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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
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