Dresden 2003 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 22: POSTER C

CPP 22.21: Poster

Donnerstag, 27. März 2003, 12:00–14:00, ZEU/250

Electrically induced morphological transitions of fluid microstructures — •Anke Klingner, Renate Nikopoulos, Stephan Herminghaus, and Frieder Mugele — Universitaet Ulm, Abt. Angewandte Physik, Albert-Einstein-Allee 11, D-89081 Ulm

Manipulating tiny amounts of liquid is a basic aim of microfluidics in which electric fields have proven to be an effective tool. We studied droplets of a partially wetting, conductive liquid on an insulating layer covering an electrode. By applying a voltage between the electrode and the liquid, the contact angle decreases following the Lippmann equation of electrowetting. For patterned electrodes, the contact angle reduction occurs only locally. We present three types of experiments: For striped electrodes an initially round droplet elongated along the stripe and adopted a No-dqlemonNo-dq shape. For suitable sizes (with respect to the electrode width) and above a certain critical voltage, droplets transformed into cylinders aligned along the electrode. This transition was recently predicted theoretically [Brinkmann et al., J.Appl.Phys. 92, 4296 (2002)]. In the second experiment, we used wedge shaped electrodes. In this case, droplets move from the narrow to the wide side of the electrode. The motion is determined by the balance of electric and pinning forces at the contact line. Finally, we investigated the stability of straight liquid channels in the saturation regime of electrowetting. The cylinders decayed by emitting small satellite droplets with a regular spacing and size distribution. All experiments were accompanied by simulations based on energy and force arguments and reflect the experimental findings.