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 work, highly ordered hexagonal mesoporous structures of aluminosilica with two different Si/Al molar ratios equal to 50 and 80 and silica samples were studied; Al was incorporated into the MCM-41 structures using the direct synthesis method, with CTAB as a surfactant.
Abstract: We report an experimental investigation of structural and adhesive properties for Al-containing mesoporous MCM-41 and MCM-41 surfaces. In this work, highly ordered hexagonal mesoporous structures of aluminosilica with two different Si/Al molar ratios equal to 50 and 80 and silica samples were studied; Al was incorporated into the MCM-41 structures using the direct synthesis method, with CTAB as a surfactant. The incorporation of aluminum was evidenced simultaneously without any change in the hexagonal arrangement of cylindrical mesopores. The porous materials were examined by techniques such as low-temperature nitrogen sorption, energy-dispersive spectroscopy, and scanning and transmission electron microscopy. Surface properties were determined through X-ray photoelectron spectroscopy, potentiometric titration, and static contact angle measurements. It was shown that an increase in surface acidity leads to an increase in the wetting energy of the surface. To investigate the influence of acidity on the con...
28 citations
TL;DR: In this article, the authors performed molecular dynamics simulations of Lennard-Jones particles confined in a parallel slit pore and found new crystal structures and proposed the complex h - T phase diagram.
27 citations
TL;DR: In this article, a flexible 1D MOF with and without guest molecules was analyzed by synchrotron powder X-ray diffraction analysis and single crystal structural analysis, which showed molecular selective sorption, which stems from guest-dependent dynamic structural transformation including pore-opening/closing processes.
Abstract: Structural analyses of a flexible 1D MOF [Cu(BF4)2(bpp)2] (bpp =1,3-bis(4-pyridyl)propane) with/without guest molecules were performed by synchrotron powder X-ray diffraction analysis and single crystal structural analysis. The guest-free MOF is composed of 1D chains composed of Cu(II) ions and bpp ligands which are accumulated to form quasi-2D layers, resulting in a quasi-layered compound. The guest-free MOF has no open pore windows; it, however, has latent quasi-hexagonal cavities surrounded by six BF4 anions. This MOF shows molecular selective sorption, which stems from guest-dependent dynamic structural transformation including pore-opening/closing processes. It shows selective alcohol sorption based on the molecular recognition properties; it sorbs C1–C3 alcohols, but not a C4 alcohol (1-butanol). Sorption properties can be enhanced by accumulation of several functionalities. In the case of the flexible MOF, the sorption properties should be synergetically enhanced by several key properties; it has m...
27 citations
TL;DR: In this article, the authors build interlayer channels formed by 2D sheets with various hydrophilicities and investigate the pressure-driven water transport via nonequilibrium molecular dynamics simulations.
Abstract: Water transport through laminated membranes composed of two-dimensional (2D) materials has gained considerable attention because of their great potential in filtration and separation applications. However, water transport between interlayers formed by 2D materials cannot be comprehensively described by traditional transport theory because different 2D materials have varying hydrophilicity, which strongly affects water transport. Herein, we build interlayer channels formed by 2D sheets with various hydrophilicities and investigate the pressure-driven water transport via nonequilibrium molecular dynamics simulations. The influence of channel hydrophilicity on water transport is dominant, especially at the nanoscale. To model the water-transport phenomena through channels with various hydrophilicities, we define a new slip length to derive the appropriate equation. By two methods of calculating the slip length based on the simulation results, we validate our derived equation, which predicts the water flux in...
27 citations
TL;DR: In this paper, the Gibbs Ensemble Monte Carlo (GEMC) simulation is used for pure components instead of the more traditional Grand Canonical Monte Carlo ensemble (GCMC) simulation to get more precise results of liquid and vapor confined pressure avoiding the phase change location determination problem.
26 citations
References
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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