Dresden 2009 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 35: Microfluidics II: Boundary conditions
CPP 35.2: Vortrag
Donnerstag, 26. März 2009, 14:30–14:45, ZEU 160
The microscopic origin of surface slip: Looking at the boundary layer of sheared liquids on solid surfaces — •Philipp Gutfreund1,2, Maximilian Wolff1,2, Stefan Gerth3, Andreas Magerl3, and Hartmut Zabel2 — 1Institut Laue-Langevin — 2Ruhr-Universität Bochum — 3Universität Erlangen-Nürnberg
According to text-book physics the contacting layer of a flowing liquid is sticking to the solid boundary and from this a smooth velocity profile develops into the bulk of the liquid, which is in agreement with many macroscopic experimental observations. However, recently, both experiments and theory have shown that on a microscopic scale simple liquids may undergo significant slip at a solid wall. Different mechanisms can be evoked to address slip like the formation of a thin depletion layer or a molecular ordering in the liquid near the interface. For most liquids, the short length scales important for slip effects are difficult to probe directly and non destructively. Grazing incident neutron scattering techniques have proved to be a very sensitive tool for the detection of depletion effects and structural arrangements close to solid-liquid walls. We will present recent results obtained by Neutron Reflectivity (NR) and Grazing Incidence Neutron Diffraction (GIND) studies on the depth profile and structure of the boundary layer of sheared hexadecane, that is known to show surface slip, on differently coated solid surfaces. The NR results for deuterated hexadecane show a depletion layer of about 2 nm and the GIND patterns show that the liquid structure factor seems to be influenced by shear.