Windscreen drying by Electrowetting

Windscreen drying by Electrowetting

Chair: Physics of Complex Fluids

Short project description:

Droplets on the windscreen of cars and airplanes impair the view of drivers and pilots. Many systems are employed to remove them, including wipers and specially coated glass. However, wipers run the risk of scratching the glass surface, while coatings are expensive, require periodic maintenance, often need to be replaced and add significant weight to an aircraft. Thus, it would be attractive to find other ways to remove droplets.

Electrowetting is the reduction of contact angle by an applied voltage. It has recently been shown that alternating current (AC) electrowetting can reduce the effective friction force acting on a droplet sliding along a solid surface, which could conceivably be used to ease the removal of droplets from windscreens. A typical electrowetting on dielectric (EWOD) setup involves a droplet of a conductive liquid sitting on a flat electrode, which is covered with a thin insulating layer; conveniently, aircraft windscreens often already incorporate electrodes for de-icing and de-fogging.

In this assignment you will investigate how EWOD with AC voltage reduces the critical angle or air flow velocity to initiate droplet motion. (Ideally, all drops will roll off the surface already in the absence of air flow.) Parameters that could be studied include the droplet size, AC frequency and amplitude, insulator roughness, and the tilt angle.

Such research could give valuable information for applying the AC EWOD effect to real airplane windscreens, where air velocities are high and droplets are blown off a tilted surface. It would also provide further information on the physics involved in the movement of droplets and thus on the movement of air-water-solid contact lines.





Tutor: Dieter ‘t Mannetje



Teacher: Frieder Mugele