Slippage at the Solid/Liquid Interface - Probing the Hydrodynamic Boundary Condition by Dewetting Experiments

Note: Pizza served at 11:45
Speaker: Oliver Bäumchen , Saarland University, Saarbrücken, Germany

When: August 11, 2009 (Tue), 11:45AM to 01:15PM (add to my calendar)
Location: SCI 352
Hosted by: Ophelia Tsui

This event is part of the Biophysics/Condensed Matter Seminar Series.

Abstract:
Understanding liquid flow in confined geometries plays a key role in the field of microand nanofluidics. Nowadays, so-called lab-on-a-chip devices open up new possibilities to perform chemical reactions or biological analysis. Thereby, friction at the solid/liquid interface strongly affects the flow dynamics. Nanoscale liquid polymer films are ideal candidates to probe the solid/liquid boundary condition: Prepared on smooth nonwettable surfaces like hydrophobized Si wafers, the films are not stable, they dewet and bead off the substrate. That way, a flow is induced without applying an external force or pumping of the liquid. The force inducing dewetting is an “internal force” and can be inferred from the effective interface potential. Probing the dynamics of the dewetting process enables us to deduce the energy dissipation by viscous flow and by friction at the solid/liquid interface. Moreover, the slip length, i.e. the extrapolation length of the velocity profile in the vicinity of a wall, can be inferred by characterizing the profile of a liquid front that is formed by the liquid while dewetting. Theoretical thin film models are applied to catch the front profile. A variation of the type of hydrophobic layer enables us to tune the boundary condition from a no-slip to a nearly full-slip condition. The experimental results concerning the slip lengths as function of viscosity and molecular weight of the polymer film will be compared to theoretical concepts.

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[5] O. BÄUMCHEN, K. JACOBS and R.FETZER, “Probing Slippage and Flow Dynamics of Thin Dewetting Polymer Films”, Proceedings of 1st Conference on Microfluidics in Bologna 2008 Dez 10-
12 ISBN 2-906831-76-X.
[6] O. BÄUMCHEN, R. FETZER, A. MÜNCH, B. WAGNER and K. JACOBS,Comprehensive Analysis of Dewetting Profiles to Quantify Hydrodynamic Slip”, IUTAM Symposium on Advances in Micro- and Nanofluidics, edited by M. Ellero, X. Hu, J. Fröhlich, N. Adams (Springer, 2009).
[7] O. BÄUMCHEN, R. FETZER and K. JACOBS, „Liquid Front Profiles Affected by Entanglementinduced Slippage”, submitted (arXiv:0907.2113v1 [cond-mat.soft]).