When a conducting liquid drop is placed on an electrode having a thin dielectric coating and an electric potential is then applied between the liquid and the electrode, the drop flattens and spreads over the electrode surface. This phenomenon is often referred to as electro-wetting. Because the phenomenon is associated with the development of an electrical charge layer, an external electric field may be used to manipulate the drops causing them to move, coalesce or break apart.
Electrowetting is a technique used to change the apparent contact angle of a dielectric fluid under the influence of electric potential. In this example, the fluid is originally hydrophobic and beads on the surface. However, when a 50V potential difference is applied, the fluid is forced to wet the surface becoming hydrophilic.
Lab-On-Chip Electro-wetting Applications
An electrowetting based Lab-on-chip that can manipulate discrete droplets allows designers to perform complex procedures similar to traditional lab apparatus but with much smaller volumes. These devices are required to efficiently transport, merge and split droplets. FLOW-3D can be a useful tool in the design process by allowing the user to simulate the effects of geometric parameters and voltages used to operate these devices.
The animations below demonstrate FLOW-3D‘s capability to simulate transport, merge and split droplets. The Lab-on-a-chip consists of two parallel plates separated by about 300μm. The bottom plate has electrodes inserted in it that are used for manipulating the droplets. The droplets are water (slightly conductive) surrounded by silicone oil. The volume of the droplet is about 800nl.
This lab-on-a-chip electrowetting simulation demonstrates an electric field being applied in order to split a small droplet.
Here an electric field is being applied in order to merge two small droplets.
This simulation shows an electric field being applied to a small droplet to control its motion.