Biomedical Engineering Reference
In-Depth Information
Figure 5. Diagram of the electrowetting setup. The pictures were taken with the system Teflon
AF1600-bmim.BF 4 -hexadecane subjected to DV voltage. Reprinted with permission from Paneru et
al. [50]. Copyright 2010 American Chemical Society.
platinum needle (the thickness and exact position of the needle turned out to be
unimportant) and external voltage was applied between the insulated electrode and
the conductive droplet.
DC voltage was obtained from a power supply and an amplifier (Trek 610D,
Medina, NY). AC voltage was generated with a signal generator (Kenwood, CR
Oscillator, AG-203). The polarity of the voltage applied to the insulated electrode
is reported. The cell was combined with a sessile drop apparatus (Fig. 5) and elec-
trowetting curves (static contact angle vs. voltage) were recorded. Voltage was
increased from zero to the maximum desired value and reduced back to zero in
various increments. A fresh electrode surface was used in every experiment.
Digital images of static droplets (624
580 pixels, 256 grey levels) were cap-
tured with a progressive scan CCD camera (JAI CV-M10BX) with a resolution of
6.7 µm/pixel. The dynamics of spreading and retraction of ionic liquid droplets was
followed with a high-speed camera (Olympus Encore MAC-2000) connected to the
same optical setup and operating at 1000 frames per second. In all cases, the droplet
silhouette was digitized and diameter and contact angle were determined by using
image processing software (ImageJ [69]).
All experiments were carried out in a class 1000 clean room at room temperature
(24 C) and normal humidity (45%).
×
C. Results
A typical electrowetting curve obtained with DC voltage for the Teflon AF1600-
bmim.BF 4 -hexadecane system is shown in Fig. 6. It is symmetric with respect to
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