Dresden 2006 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 24: POSTER Microfluidics
CPP 24.4: Poster
Donnerstag, 30. März 2006, 17:00–19:00, P2
Wettability-control of droplet deposition and detachment — •Jean-Christophe Baret1 and Martin Brinkmann2 — 1Institut Charles Sadron, 6, rue Boussingault, F-67083 Strasbourg, France — 2Max-Planck-Institut for Dynamics and Self-Organization, Bunsenstr. 10 D-37073 Goettingen, Germany
The conditions for droplet deposition on a plane surface are studied using the electrowetting effect to continuously modulate the substrate wettability. Droplets of various volumes attached to the tip of a pipette are brought into contact with the surface. When pulled up the droplets are deposited at sufficiently small contact angles and large volumes or completely detach from the substrate at small volumes and large contact angles. We demonstrate that electrowetting on dielectric (EWOD) provides an ideal tool to systematically study capillary instabilities involving a free contact line. The experimental limit between deposition and detachment in the contact angle/volume plane is in good agreement with analytical and numerical predictions obtained within the capillary model. In the case of zero buoyancy, the droplet contour can be expressed in terms of elliptic integrals which allows to derive an approximate expression for the droplet volume at the transition between the two modes of instability. This criterion can be applied in technological processes which involve the production and placement of small droplets, e.g., in spotting arrays of biomolecules or in microcontact printing.