Adsorption and Phase Transitions in Slit-like Pores with Differently Adsorbing Walls.
We study the adsorption of a lattice gas in a slit-like pore with different walls. The density profiles are evaluated in the framework of the mean-field approximation. We show that changes in the potential field exerted by one wall can lead to substantial modifications of the phase behavior of the fluids. Copyright 2001 Academic Press.
Two-stage capillary condensation in pores with structured walls: A nonlocal density functional study
We present phase diagrams for capillary condensation in chemically structured slit pores characterized by two first-order transitions from the confined “gas” over “liquid bridges” to “liquid.” The split adsorption is produced by a complex periodic wall potential in one of the lateral directions that mimics inhomogeneities in real materials. After the previous condensation of liquid drops at the most attractive adsorption sites these may combine to form liquid bridges between opposite walls, separated between them by “gas gaps.” Nonlocal density functional theory is employed to investigate this stepwise mechanism and the stability of the liquid bridges phase in function of the thermodynamic conditions and the pore structure, especially the ratio of the two typical lengths, the corrugation period λ and the pore width H. Macroscopic predictions for the subcritical phase equilibria and the critical limit complete the study. The calculations confirm our previous results [P. Rocken and P. Tarazona, J. Chem. Phy...
Wetting and domain-growth kinetics in confined geometries.
In this paper, we review the theoretical and experimental progress in understanding the controversial phase behavior of binary liquids in dense porous media. Experimental observation of metastability and hysteresis in the phase-separation behavior has led to two widely different theoretical interpretations: the random-field Ising picture and the single-pore picture. We argue that the random-field model is inapplicable to binary liquids in low-porosity media such as Vycor, and discuss the available experimental evidence on such systems. Next, we present Monte Carlo studies of phase-separation kinetics of an Ising model in a pore. We find that the domain-growth kinetics slow down dramatically once the domain size becomes comparable to the pore size, as predicted by the single-pore model. In addition, we examine the influence of temperature and interfacial phase transitions on the kinetics, and show that the domain-growth rate slows down as the temperature moves further into the two-phase region. Finally, our results for small pores, only 20 spins across, suggest that macroscopic descriptions are surprisingly successful, even at short length scales.