Nanotube Coatings Relieve Driver Frustration

An electrically conductive coating that uses nanotechnology to heat a car's windshield -- but has no wires to obstruct the view -- could make fogged-up windshields a thing of the past.

On cold winter mornings, a driver’s vision is often blurred by moisture collecting on the inside of the windshield. This happens when warm, humid air comes into contact with a cold surface. At a particular temperature, known as the dew point, the moisture in the air condenses and forms a layer on the colder surface; it frequently happens to a glass containing a cold drink or the bathroom mirror after a shower.

Fogged-up windshields are a potential hazard. In the future, a heatable coating made of carbon nanotubes could keep windshields clear. (Photo: ©Fraunhofer TEG)

Cold air is not able to contain as much moisture as warm air, something that is much more noticeable in small spaces -- like in a car. Condensation can be prevented by increasing the volume of air (opening the windows), by heating the vehicle’s entire interior, or by heating at least the windshield to a temperature above the dew point.

Ivica Kolaric of the Fraunhofer Technology Development Group TEG in Stuttgart favors the third option. His new process warms up the windshield -- not with costly copper heating elements, but instead with a transparent coat of carbon lacquer, made up of carbon nanotubes. Kolaric and his team are currently working on a bonding system which, in a year or two, could keep not only windshields but also bathroom mirrors free from condensation.

When attached to an electricity supply, the lacquer coating is transformed into a wide, flat heater which exactly covers the surface to be heated and continues to function even when it is damaged in places. If a heated windshield containing wire heating elements is chipped by a stone, for example, and one of the wires is severed, the entire heater could very well cease to function because of the interruption to the current. For the carbon nanotube heater, however, a few small defects in the coating are not a problem because the current flows over the entire surface.

Another advantage of the “flat” conductor is its uniform heat distribution. Every single point on the surface of the windshield is heated evenly, rather than the warmth radiating outwards from the heating elements. The nanotube coating itself does not store any heat.

“The lacquer converts the electricity almost entirely into warmth and transfers this to the windshield,” said Kolaric. The windshield is clear in a very short time with minimal power consumption. “What’s more, the CNT (carbon nanotube) resistance heater can be integrated in the vehicle’s standard 12-volt power supply,” he said.

For more information, visit: www.fraunhofer.de/fhg/EN/press/index.jsp