EMLG-JMLG Annual Meeting 2010

Complex liquids: Modern trends in
exploration, understanding and application

European Molecular Liquids Group (EMLG)    Japanese Molecular Liquids Group (JMLG)
Institute for Condensed Matter Physics of National Academy of Sciences of Ukraine

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Organisation for the Prohibition of Chemical Weapons

Scaled particle theory for a hard-sphere fluid confined in different model matrices

W. Dong

Despite intense investigations during the last two decades, no analytical result has been available for any non trivial off-lattice model for fluids in random porous media until very recently. In a recent work [1, 2], we presented a first formulation of scaled particle theory (SPT) for a hard sphere fluid in a hard sphere matrix or in an overlapping hard sphere matrix. The agreement between this SPT and simulation [3] is fine (errors ≤ 20% ). However, we have identified some inconsistencies in this first formulation of SPT (named as SPT1 hereafter). For example, in the limit of one single big matrix particle, i.e., R₀ → ∞ (R₀: radius of matrix particle), ρ₀ → 0 (ρ₀: matrix density) with η₀ remaining finite (η₀ = 4πρ₀R₀³/3), the fluid-matrix system becomes in fact a fluid in contact with a flat hard wall. In this case, the fluid chemical potential, µ₁, the fluid pressure, P, and the contact fluid-fluid radial distribution function, g₁₁(2R₁) (R₁: radius of fluid particle), should reduce to their corresponding results for a bulk fluid and ρ₁g₁₀(R₁+R₀)=P should hold (ρ₁: fluid density; g₁₀(R₁+R₀): contact fluid-matrix radial distribution function). SPT1 does not give the appropriate results in the limit of one single big matrix particle. In this presentation, we will show how these inconsistencies in SPT1 can be remedied and give a new formulation of SPT (named as SPT2) for a HS fluid in a HS matrix or in an overlapping HS matrix [4].

We carried out also some grand canonical ensemble Monte Carlo simulations in order to make more extensive comparison with our SPT2. In the majority of cases, SPT2 improves significantly the accuracy of different thermodynamic properties. We will briefly talk about also the possible extension of SPT2 to multi-component systems and some specific difficulties in these cases.

References

1. M. Holovko and W. Dong, “A highly accurate and analytic equation of state for a hard sphere fluid in random porous media”, J. Phys. Chem. B, 113, 6360, (2009).
2. W. Chen, W. Dong, M. Holovko and X.S. Chen, Comment on “A highly accurate and analytic equation of state for a hard sphere fluid in random porous media”, J. Phys. Chem. B (in press).
3. A. Meroni, D. Levesque and J.J. Weis, J. Chem. Phys. 105, 1101 (1996).
4. T. Patsahan, M. Holovko and W. Dong, “Fluids in porous media: Scaled particle theory”, (publication in preparation).