Dresden 2009 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 35: Microfluidics II: Boundary conditions

CPP 35.3: Vortrag

Donnerstag, 26. März 2009, 14:45–15:00, ZEU 160

Altering the boundary conditions to influence flow dynamics of a liquid film — •Matthias Lessel, Oliver Bäumchen, and Karin Jacobs — Saarland University, Experimental Physics, D-66041 Saarbrücken

In the course of the miniaturization of fluidic devices, the typical diameter of flow channels becomes smaller and smaller. Typically, the velocity of the liquid at the boundary to a channel wall is zero, a parabolic velocity profile is measured and high pressure is needed to move the liquid.

We study the impact of surface modifications on the slip length on a model system: polymer films on tailored Si wafers. To induce flow we use the dewetting process, which is driven by an internal force governed by the effective interface potential. In our case, hydrophobic substrates (Si wafers covered by octadecyltrichlorosilane (OTS), dodecyltrichlorosilane (DTS), or Teflon (AF1600)) are only partial wetted by the polystyrene melt. They are ideal smooth substrates. So, roughness effects could be neglected.

Using optical microscopy we found at constant temperature an increase of the dewetting velocity on substrates which show slippage. The slip lengths could be calculated by observing the growth of dewetting holes in the film. The slip lengths lay in the range from several nanometers for AF 1600 to several micrometers for DTS. These results could be approved by analyzing the rim shapes around the holes using AFM. The shapes were found to be influenced by slippage too.