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The critical properties of the Lennard-Jones fluid in slitlike pores of different widths have been studied by the Gibbs ensemble Monte Carlo method and the lattice gas model. Graphite pores up to 10 molecular diameters in width and similar pores with weaker solid−fluid interactions have been considered. Strong layering of the adsorbate in the graphite pores confirmed the applicability of the lattice gas model to such systems. The vapor−liquid phase diagrams for the confined fluids obtained with the two methods are in reasonable agreement with each other. Linear dependence of the critical temperature on the inverse pore width was found. It is demonstrated that the critical temperature may depend strongly on the strength of the sold−fluid interactions. The lattice gas model showed nonmonotonic dependence of the critical density on the pore width.

In this work the two phase coexistence region for simple fluids confined within slit and cylindrical pores is investigated. The format of this study involves a comparison of the results obtained with the aid of lattice models and molecular dynamics simulations in the near-critical region, and it is shown that the shape of the phase diagram which may be observed depends not only on pore geometry but also on the relative strengths of the fluid-wall and fluid-fluid interaction potentials. In comparison of the results predicted by lattice-gas theory and molecular dynamics simulation, it is found that the lattice model correctly accounts for all of the general features of the phase diagram arising from fluid-wall interaction potential, pore size, and pore shape. In the critical region however there are quantitative disagreements between lattice theory and molecular simulation due primarily to the mean-field nature of the quasichemical approximation employed in the lattice-gas calculations. Modifications of the lattice model computations which improve the agreement with simulation are presented and discussed.

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