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19 January 2006 Droplet manipulation for lab-on-a-chip using electrowetting
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Electrowetting, the phenomena of changing interfacial energy of an interface, has been demonstrated to be an excellent actuation and pumping mechanism for microfluidics and lab-on-a-chip applications. Individual droplets can be moved and deformed on microchips using voltages as low as 15V. In electrowetting, application of a voltage across the electrodes of a micro-droplet causes it to change the interfacial energy of solid-liquid interface which in turn changes the contact angle of the liquid on the solid. The contact angle is a measure of the extent of wetting of the liquid on the surface. In conventional electrowetting, it has been found that the polarity of the applied potential does not affect the contact angle change. However, our experimental results show that the change of polarity across the electrodes of a micro-droplet can reverse the contact angle change. We call this phenomenon 'dewetting'. The actual physics behind this still remains unexplored. In our experiments we used 100 nm of aluminium on a silicon substrate to form the bottom electrode. A 60 nm silicon dioxide or a 1.4 μm thickness strontium doped lead zirconium titanate (PSZT) layer was used as the dielectric and 380 nm of Teflon was used to make a hydrophobic surface. A platinum wire, which was inserted into the micro-droplet, formed the top electrode. The highest dewetting contact angle change was found to be 9o for a 5μl droplet at 60 V. This compared to a maximum of 41o which we obtained for conventional electrowetting.
© (2006) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
T. Mahmud, G. Rosengarten, and A. Holland "Droplet manipulation for lab-on-a-chip using electrowetting", Proc. SPIE 6036, BioMEMS and Nanotechnology II, 60361Z (19 January 2006);

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