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Berlin 2005 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 30: POSTER: Chemical physics

CPP 30.27: Poster

Tuesday, March 8, 2005, 16:30–18:30, Poster TU D

Phase behavior of confined asymmetric binary liquid mixtures: Theoretical analysis of experimental data — •Dirk Woywod, Gernot Rother, Sebastian Schemmel, Gerhard H. Findenegg, and Martin Schoen — Stranski-Laboratorium, TU Berlin, Sekr. TC 7,Straße des 17. Juni 124, 10623 Berlin

We investigate the phase behavior of an asymmetric binary liquid mixture between two planar homogenous substrates (slit pore). We employ a lattice-gas model and a mean-field approximation to obtain a closed expression for the grand potential.

This model is applied to study the phase behavior and microscopic structure of a iso-butyric acid (iBA) + heavy water (D2O) liquid mixture confined to mesoporous silica matrices (CPG-10). Confinement-independent model parameters are adjusted to match the experimental coexistence curve in the bulk. Since the pore liquid is in equilibrium with an external reservoir we can also fix the thermodynamic state in the model. By choosing appropriate values of the pore width and the attraction strength between substrates and water we analyze the impact of confinement on the phase diagram. Apart from a depression of the liquid+liquid critical point we observe surface-induced phase transitions as well as water adsorption by the walls [1]. The theoretical predictions are supported by differential refractometry data and small-angle neutron scattering measurements.

 [1] D. Woywod, S. Schemmel, G.H. Findenegg, and M. Schoen, J. Chem. Phys., (sub. 2004)

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