A new kind of polymer that changes color at the flip of an electrical switch has been invented by a University of Rhode Island chemist.

Sze Cheng Yang demonstrated his invention for reporters last week in his South Kingston laboratory. The polymer was formed into a thin coating on a piece of glass, making it green. Yang connected a flashlight battery to electrodes on the glass. Waves of color rippled across the sheet for a few seconds until it turned solid blue. A second battery doubled the voltage and turned the glass purple.

Yang said the glass could be used as windows that turn into shades. He said it should also be possible to apply the polymer to automobile bodies to make cars that change color.

The coating changes color because it contains a thin layer of long polymer molecules that fold into different shapes depending on the voltage applied.

Any object's color depends on the wavelengths of light it reflects or absorbs. White light is a mixture of all colors but if it falls on a surface that absorbs everything but blue, the object will look blue. Yang said the shapes of the molecules determine which wavelengths of light they absorb or reflect.