Electrowetting

 

 

Electrowetting Actuation:

 

Electrowetting is a phenomenon in which the contact angle of a polarizable/conductive liquid drop is manipulated by the means of applying an electric potential between the drop and the electrode on which the drop is placed. In this manner, the electrode must be coated with an insulator (dielectric) covered subsequently by a hydrophobic coating. This phenomenon can be used to manipulate and move liquid droplets in digital microfluidics and Lab-On-A-Chip technologies. It can also be used to move the droplets to a hot-spot and transfer heat to avoid the concentration of heat in a very small area on a transistor or integrated circuit.

 

Using a PCB-based electrowetting device, the contact angle of a droplet is manipulated under various values of applied AC voltages. Also an in-house numerical code is developed to simulate electrowetting using VOF method. The images taken from the experiments and simulations are compared. Experiments are performed both in air and silicone oil environments.

 

Electrowetting on Dielectric

 

Calculated images (a) and experimental results for (b) air and (c) silicone oil environments for a 20 μL mercury droplet under the effect of various applied 50 Hz AC voltages. Numerical results involve the electric potential contours and the black line shows the free surface of the droplet.

 

 

 

Digital Microfluidics:


As mentioned above, electrowetting can also be used in digital microfluidics where single drops can be manipulated using an applied voltage to move along an array of electrodes. Figure below shows the movement of a mercury drop along an array of 1 mm electrodes which are placed 300 μm appart. When the 240V voltage is applied to the adjacent electrode, the contact angle of the drop will change and as a result, the drop will move toward that electrode.

 

 

DigitalMicrofluidic 

Experimental results of a mercury drop moving along an array of electrodes in digital microfluidics. Hold the mouse cursor on the image to see the movie.

 

 

parallel22new

Experimental results of a mercury drop, sandwiched between two parallel plates, moving along an array of electrodes (the droplet diameter is 1.6mm)

 

parallel11new

Experimental results of a mercury drop, sandwiched between two parallel plates, moving along an array of electrodes (the droplet diameter is 3.2mm)

 

The Electrowetting Actuation of a droplet confined in a Channel:


The experimental investigation of Electrowetting actuation of a microdrop confined in a mili/microchannel is our current research topic of interest. This phenomenon can be utilized in electronics cooling, micropumping, microswitches, microvalves and so on. Figures below show the electrowetting actuation of a mercury drop confined in a channel with the width and heigth of 2 and 1 millimeters, respectively.

 

channel11
Experimental results of a mercury drop, confined in channel, moving along an array of electrodes

 

channel22

Experimental results of a mercury drop, confined in channel, moving along a Y junction (this design can be used as a droplet splitter or a microvalve)

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