Modeling of Random Formation of Microporous Material Following Thermodynamic Limitations.
The problem of pore formation in limited (small) volume has been considered. General equations describing the system in the continuous (many particles) and discrete (few particles) cases have been obtained. It has been shown that pore formation is not limited by nucleus genesis because of entropic reasons. Kinetic limitation leads to the auto-acceleration-like form of the dependence of the number of empty cells and the internal area functions. The percolation problem has been solved for 2- and 3-dimensional cases with comparison of systems obtained by traditional Monte Carlo and thermodynamic factors. The 3-dimensional situation leads to reduction of the percolation threshold. However, the difference in the values of percolation thresholds estimated by the ordinary Monte Carlo simulation and with thermodynamic limitation is not significant (less than the eventual error). The change of tortuosity was estimated. At the percolation threshold, the tortuosity decreases rapidly, then very slowly with an increase in microporosity, and only at very high microporosity (close to 1) the decrease in tortuosity is again sharp. The influence of the thermodynamic limitation on the regularity of the micropore cluster has been analyzed based on the consideration of behavior of free energy and surface area of the cluster. It has been found that both of these structural parameters significantly decrease if the thermodynamic limitation is imposed. Copyright 1999 Academic Press.
Romm
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Chemical Engineering Department, Technion-IIT, Haifa, 32000, Israel