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 article, a procedure for the reliable and reproducible formation of monodispersed polymer nanocrystals whose morphologies can be easily controlled to produce structures ranging from nanoparticles to nanorods was developed.
Abstract: We developed a procedure for the reliable and reproducible formation of monodispersed polymer nanocrystals whose morphologies can be easily controlled to produce structures ranging from nanoparticles to nanorods. The directional cooling crystallization of ferroelectric polymer solutions under nanoconfinement allowed polyvinylidene fluoride to form single crystalline monodisperse nanocrystals without the use of surfactants or stabilizers. An important growth condition necessary to yield highly crystalline ferroelectric polymers was a regulated thermal gradient under nanoconfinement to induce uniform nucleation and controlled directional growth. While other methods involving the nanoconfined crystallization of polymers are restricted to yield nanofibers or nanotubes with a high aspect ratio, our unidirectional cooling method produced nanocrystals of ferroelectric polymers with nanosphere, nanocapsule, and nanorod structures. Field-emission scanning electron microscopy, transmission electron microscopy, dyna...
19 citations
TL;DR: In this paper, the melting behavior of aniline confined within an activated carbon fiber having slit-shaped pores was investigated. And the authors used dielectric relaxation spectroscopy to determine the transition temperatures of the anilines and also the dielectrics relaxation times over the temperature range 240 to 340 K.
Abstract: We report both experimental and molecular simulation studies of the melting behavior of aniline confined within an activated carbon fiber having slit-shaped pores. Dielectric relaxation spectroscopy is used to determine the transition temperatures and also the dielectric relaxation times over the temperature range 240 to 340 K. For the confined system two transitions were observed, one at 298 K and a second transition at 324 K. The measured relaxation times indicate that the low temperature phase (below 298 K) is a crystalline or partially crystalline solid phase, while that above 324 K is a liquid-like phase; for the intermediate phase, in the range 298–324 K, the relaxation times are of the order 10−5s, which is typical of a hexatic phase. The melting temperature of the confined system is well above that of bulk aniline, which is 267 K. The simulations are carried out using the Grand Canonical Monte Carlo method together with Landau free energy calculations, and phase transitions are located as...
18 citations
TL;DR: The effect of pore size on capillary condensation and solid-liquid phase changes of ammonia in MCM-41 and SBA-15 was studied by adsorption and FTIR measurements of condensed phases at low temperatures, suggesting that this is a universal phenomenon among fluids in mesopores.
Abstract: The effect of pore size on capillary condensation and solid-liquid phase changes of ammonia in MCM-41 and SBA-15 was studied by adsorption and FTIR measurements of condensed phases at low temperatures. Adsorption isotherms are all typical type IV on the fully hydroxylated surfaces, without hysteresis loops in the smaller pores (d < 2.4 nm). In the larger pores, hysteresis loops appear at lower temperatures and disappear with increasing temperature, i.e., the capillary critical phenomenon was detected (hysteresis critical point). The criticality of the adsorption hysteresis loop is very similar to that for nonpolar nitrogen in mesopores of various shapes, suggesting that this is a universal phenomenon among fluids in mesopores. Freezing and melting of capillary-condensed ammonia were observed by FTIR spectroscopy. The melting temperature of capillary-condensed ammonia decreased with decreasing pore size, which is similar in the behavior of freezing. In the smaller pores (d < 2.4 nm); however, ammonia was not frozen. It is suggested that the capillary-condensed inner part, i.e., inside the ammonia monolayer, is affected too much by the pore wall and/or is too small in volume to crystallize. In the larger pores of SBA-15, crystallization is remarkably segregated from ammonia molecules strongly coordinated to surface hydroxyls.
18 citations
TL;DR: A hybrid theoretical study for unraveling the regulation mechanism by combining classical density functional theory (CDFT) with machine learning (ML) and sets up a feasible platform for investigating complex interfacial systems with multiple controlling parameters.
Abstract: Geometrical confinement has a large impact on gas solubilities in nanoscale pores. This phenomenon is closely associated with heterogeneous catalysis, shale gas extraction, phase separation, etc. W...
17 citations
TL;DR: In this paper, the authors review recent progress made concerning the modelling of equilibrium gas mixture adsorption in activated carbons and show that for less demanding scenarios, i.e. relatively simple gas mixtures adsorbed at supercritical temperatures, current methods are satisfactory.
Abstract: We review recent progress made concerning the modelling of equilibrium gas mixture adsorption in activated carbons. Much of the discussion focuses on modern statistical mechanical methods, such as classical density functional theory and Monte-Carlo simulation, as well as the surface models employed, i.e. the surface characterisation, and we confine our attention to work that has been compared quantitatively with experiment. We will see that for less demanding scenarios, i.e. relatively simple gas mixtures adsorbed at supercritical temperatures, current methods are satisfactory. But further developments in our models and theories are probably needed to describe the adsorption of more complex adsorbates such as those involving water at room temperature.
17 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