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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 18: Poster: Colloids and Complex Fluids

CPP 18.5: Poster

Montag, 20. März 2017, 18:30–21:00, P1C

Characterization of Marangoni convections in microchannel structures — •Daniel Zapf, Michael Orlishausen, Lorentz Butzhammer, and Werner Köhler — Physikalisches Institut, Universität Bayreuth, 95440 Bayreuth, Germany

We have investigated Marangoni convection at the meniscus formed by a liquid-gas interface in microchannel structures with characteristic length scales of the order of 100 µ m. In ethanol-water mixtures Marangoni convection is driven both by temperature and composition gradients, in pure ethanol by temperature gradients alone. The temperature and concentration differences arise instantaneously from inhomogeneous evaporation at the liquid-gas interface but can also be induced and switched by selective laser heating. The resulting flows are visualized by polystyrene tracer particles of 600 nm in diameter under a light microscope. Particle velocities are determined via image correlation techniques. As a function of the meniscus shape, the microchannel geometry and the evaporation rate of the volatile component, either a single or two symmetric convection roles are observed. They come to a sudden halt when the evaporation of the liquid is stopped by an increas of the vapor pressure in the gas phase. Currently we are working on the pressure measurement in the microchannels. Tracer particles are repelled from stream lines that come closer to the meniscus than one particle radius. Surprisingly, this leads to large depletion zones and very efficient particle accumulation inside the vortex. We will present a quantitative analysis of the flow patterns and numerical simulations of the development of the depletion and accumulation zones.