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.
Citations
More filters
TL;DR: In this paper, a Grand canonical Monte Carlo simulation of soft spheres in slit nanopores is used to investigate the formation of frozen phases, which give rise to a sequence of solid-solid transformations as the pore width is varied.
Abstract: Freezing of soft spheres in slit nanopores is investigated using Grand canonical Monte Carlo simulations. The pores are in equilibrium with a liquid located close to the liquid–solid coexistence region in the bulk Lennard-Jones phase diagram. In addition to layering, the confined fluid is found to possess in-plane order, leading to the formation of frozen phases which give rise to a sequence of solid–solid transformations as the pore width is varied. Transformations between n layered triangular to n+1 layered square lattices and between n layered square to triangular lattices, are observed for n=1, 2, 3, and 4. The transition from triangular to square lattices occurs via an intermediate buckled phase which is characterized by increased out-of-plane motion, while maintaining in-plane triangular order. Buckling was found to decrease with increasing number of layers. The transition between square to triangular lattices at a fixed number of layers is accompanied by a lowering of the solvation force, resulting in a doublet in the solvation force maxima. Influence of fluid–wall interactions on the nature of the frozen phases are studied by comparing the structures formed with a 10-4-3 and 10-4 fluid–wall potential. The solid structures are classified based on their closest 3D counterparts.
61 citations
TL;DR: A molecular-simulation study of the pressure tensor of argon confined in slit-shaped nanopores with walls of various models, including carbon and silica materials shows that the pressure is strongly enhanced by confinement, arising from the effect of strongly attractive wall forces.
Abstract: Experiments and simulations both suggest that the pressure experienced by an adsorbed phase confined within a carbon nanoporous material can be several orders of magnitude larger than the bulk phase pressure in equilibrium with the system. To investigate this pressure enhancement, we report a molecular-simulation study of the pressure tensor of argon confined in slit-shaped nanopores with walls of various models, including carbon and silica materials. We show that the pressure is strongly enhanced by confinement, arising from the effect of strongly attractive wall forces; confinement within purely repulsive walls does not lead to such enhanced pressures. Simulations with both the Lennard-Jones and Barker-Fisher-Watts intermolecular potentials for argon-argon interactions give rise to similar results. We also show that an increase in the wall roughness significantly decreases the in-pore pressure due to its influence on the structure of the adsorbate. Finally, we demonstrate that the pressures calculated from the mechanical (direct pressure tensor calculations) and the thermodynamic (volume perturbation method) routes yield almost identical results, suggesting that both methods can be used to calculate the local pressure tensor components in the case of these planar geometries.
61 citations
TL;DR: Using molecular dynamic simulations, a waterlike model confined between two fixed hydrophobic plates is studied and it is observed that in the pressure-temperature phase diagram the temperature of maximum density and theTemperature of maximum and minimum diffusion occur at lower temperatures when compared with the bulk values.
Abstract: Using molecular dynamic simulations we study a waterlike model confined between two fixed hydrophobic plates. The system is tested for density, diffusion, and structural anomalous behavior and compared with the bulk results. Within the range of confining distances we had explored and observed that in the pressure-temperature phase diagram the temperature of maximum density (TMD line) and the temperature of maximum and minimum diffusion occur at lower temperatures when compared with the bulk values. For distances between the two layers below a certain threshold, d ⩽ dc, only two layers of particles are formed, for d ⩾ dc three or more layers are formed. In the case of three layers the central layer stays liquid while the contact layers crystallize. This result is in agreement with simulations for atomistic models.
60 citations
TL;DR: NMR relaxation time measurements showed that the dynamics of the confined liquids are slower than those of the bulk above its melting point, and the activation energies of reorientation motions in the confined phases, determined from spin lattice relaxation times, are smaller than the bulk ones.
Abstract: We used differential scanning calorimetry, neutron scattering, and proton NMR to investigate the phase behavior, the structure, and the dynamics of benzene confined in a series of cylindrical mesoporous materials MCM-41 and SBA-15 with pore diameters, d, between 2.4 and 14 nm. With this multitechnique approach, it was possible to determine the structure and, for the first time to our knowledge, the density of confined benzene as a function of temperature and pore size. Under standard cooling rates, benzene partially crystallizes in SBA-15 matrixes (4.7
60 citations
TL;DR: In this paper, the freezing point of the PEG intercalated into the shaped composite paper was successively decreased down to room temperature, while the melting point was kept constant with that of bulk PEG, which means controlled heat release was thus achieved.
Abstract: Brick-and-mortar microstructures of graphene oxide–polyethylene glycol (PEG) composite papers were easily prepared with large area. The freezing point of the PEG intercalated into the shaped composite paper could be successively decreased down to room temperature, while the melting point was kept constant with that of bulk PEG, which means controlled heat release was thus achieved.
57 citations
References
More filters
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 1995TL;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
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