Berlin 2008 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 22: POSTERS Micro- and Nanofluidics

CPP 22.10: Poster

Mittwoch, 27. Februar 2008, 16:00–18:30, Poster A

Probing slippage of thin polymer films on smooth hydrophobic surfaces — •Oliver Bäumchen, Renate Fetzer, and Karin Jacobs — Saarland University, Experimental Physics, D-66123 Saarbrücken, Germany

We study the boundary conditions at the solid/liquid interface of thin film flow of highly viscous Newtonian liquids. To induce flow, we make use of the dewetting process. In our system, polystyrene melts below the entanglement length dewet after annealing above their glass transition temperature from smooth hydrophobic substrates, silicon wafers covered by octadecyltrichlorosilane (OTS), dodecyltrichlorosilane (DTS) brushes, and thin teflon (AF1600) films. By investigating the radii of the growing holes, we find that the dewetting velocity at a certain temperature strongly depends on the type of substrate. Identifying viscous flow and slippage contribution allows us to extract the slip length. The numbers for the slip length are consistent with results obtained from atomic force microscopy analysis of the shape of the rims that surround each hole. They exhibit either an oscillatory or a monotonically decaying rim profile. A recently developed Stokes model for a thin liquid film dewetting from a solid substrate [1], which is not restricted to a certain range of slip lengths, is used to determine slip length as well as the viscosity of the polymer melt. The slip length on the silane brushes is found to be about one order of magnitude larger on DTS than on OTS and decreases with increasing temperature, whereas on AF1600 we find a nearly vanishing contribution of slippage. [1] R. Fetzer et al., Langmuir 23 (2007) 10559.