Berlin 2008 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
CPP: Fachverband Chemische Physik und Polymerphysik
CPP 22: POSTERS Micro- and Nanofluidics
CPP 22.5: Poster
Mittwoch, 27. Februar 2008, 16:00–18:30, Poster A
Topology transitions of monodisperse emulsions in microchannels — •Enkhtuul Surenjav1, Martin Brinkmann1, Craig Priest1, Stephan Herminghaus1, and Ralf Seemann1,2 — 1MPIDS, D-37073, Göttingen, Germany — 2Saarland University, D-66041, Saarbrücken, Germany
In the confinement of a micro-channel, foam-like emulsions appear in a variety of periodic patterns, we call topologies. Transitions between certain topologies in a flowing emulsion can be induced through variations of the channel geometry. Such a `passive' manipulation of the droplets by means of the confinement allows to position, sort, exchange, compile and redistribute droplets. These rearrangements are studied for various geometries as a function of volume fraction and droplet size. Based on numerical and analytical result we predict mechanical instabilities in straight channels and present a phase diagram for the different droplet topologies. Furthermore, we quantify the impact of a bend in the channel on the exchange of droplet positions. In combination with a technique to coalesce targeted pairs of droplets, a controlled interchange of neighboring droplets can be used to perform multi-step reactions. The transition between a bamboo and a zigzag structure demonstrates that topology transitions are inherently hysteretic at large volume fractions of the dispersed phase. `Passive' reorganizations based on fixed channel geometries can be supplemented by `active' manipulation of an incorporated ferrofluid phase. A ferromagnetic continuous phase facilitates reorganization of liquid compartments on demand using an electromagnetic trigger.