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Regensburg 2004 – scientific programme

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DY: Dynamik und Statistische Physik

DY 17: Fluids II

DY 17.5: Talk

Monday, March 8, 2004, 17:30–17:45, H3

Adsorption of an asymmetric binary mixture at a selective solid wall — •Dirk Woywod, Jörg Silbermann, and Martin Schoen — Stranski-Laboratorium für Physikalische und Theoretische Chemie
TU Berlin
Sekretariat TC 7
Strasse des 17.Juni 124
10623 Berlin

We consider a binary (A-B) mixture fluid near a selective planar homogenous wall. Using a lattice-gas model and mean-field approximation to the intrinsic free-energy functional, we obtain a closed expression for the potential density in the grand canonical ensemble (V,TAB). This expression depends on the attraction strength of the fluid-fluid interactions (єAABB, єAB), the fluid-wall interactions (єAWBW), and the local densities (ρA, ρB). Minimizing the potential density numerically gives us access to complete phase diagrams including wetting films [1].
In this presentation, we choose bulk parameters in order to promote the formation of demixed A-rich liquid phases near coexistence with a gas phase. Introducing a preference of the wall for molecules of component B, first-order phase transitions between adsorbed mixed, A-rich and B-rich films are observed. Besides multiple surface critical points, we also find a peculiar temperature dependence of the concentration of component B within a B-rich mixed film.[2]
 [1] D. Woywod, M. Schoen, Phys. Rev. E 67, 026122 (2003)
 [2] J. Silbermann, D. Woywod, M. Schoen, Phys. Rev E, in press (2003)

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