Modeling of Adsorption in Finite Cylindrical Pores by Means of Density Functional Theory |
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Authors: | E A Ustinov D D Do |
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Institution: | (1) Saint Petersburg State Technological Institute, Technical University, 26 Moskovsky, Prospect, Russia, 198013;(2) Department of Chemical Engineering, University of Queensland, St. Lucia, Queensland, Australia, 4072 |
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Abstract: | Adsorption of argon at its boiling point in finite cylindrical pores is considered by means of the non-local density functional
theory (NLDFT) with a reference to MCM-41 silica. The NLDFT was adjusted to amorphous solids, which allowed us to quantitatively
describe argon adsorption isotherm on nonporous reference silica in the entire bulk pressure range. In contrast to the conventional
NLDFT technique, application of the model to cylindrical pores does not show any layering before the phase transition in conformity
with experimental data. The finite pore is modeled as a cylindrical cavity bounded from its mouth by an infinite flat surface
perpendicular to the pore axis. The adsorption of argon in pores of 4 and 5 nm diameters is analyzed in canonical and grand
canonical ensembles using a two-dimensional version of NLDFT, which accounts for the radial and longitudinal fluid density
distributions. The simulation results did not show any unusual features associated with accounting for the outer surface and
support the conclusions obtained from the classical analysis of capillary condensation and evaporation. That is, the spontaneous
condensation occurs at the vapor-like spinodal point, which is the upper limit of mechanical stability of the liquid-like
film wetting the pore wall, while the evaporation occurs via a mechanism of receding of the semispherical meniscus from the
pore mouth and the complete evaporation of the core occurs at the equilibrium transition pressure. Visualization of the pore
filling and empting in the form of contour lines is presented. |
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Keywords: | density functional theory adsorption capillary condensation MCM-41 |
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