Regensburg 2007 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 24: Micro and Nano Fluidics II: Soft Objects in Flow + Slippage

CPP 24.9: Talk

Thursday, March 29, 2007, 12:00–12:15, H37

Impact of the solid/liquid interface on the flow dynamics of thin polymer films — •Oliver Bäumchen, Renate Fetzer, and Karin Jacobs — Saarland University, Experimental Physics, D-66041 Saarbrücken, Germany

We investigate the boundary conditions at the solid/liquid interface of thin film flow of highly viscous Newtonian liquids. To induce flow, we use the dewetting process which starts by the nucleation of holes. In our system, low molecular weight polystyrene melts dewet from hydrophobic substrates after annealing above their glass transition temperature. By investigating the radii of growing circular holes, we find that the dewetting velocity at a constant temperature strongly depends on the type of substrate. We could show that in the case of silicon wafers covered by different silane brushes (octadecyltrichlorosilane and dodecyltrichlorosilane) hole growth can be described by a superposition of viscous flow and slippage. A novel data analysis method is used to identify the two velocity contributions, viscous flow and slippage, and to extract the slip length. The numbers for the slip length are consistent with results obtained from SPM analysis of rim profiles [1]. This latter method could be connected to a lubrication model derived from the Navier-Stokes equations with a Navier-slip condition and enables us to determine the slip length as well as the viscosity of the polymer melt. The variation of further system parameters such as substrate properties allows us to obtain more detailed information about the mechanism of slippage at the interface on a molecular level. [1] R. Fetzer et al., Europhys. Lett. 75 (2006) 638