May 8, 2006—A new conductive plastic that changes color in response to an electric field could be put to use in products ranging from hue-switching camouflage gear to flexible computer displays.
The electrochromic polymers, developed by Greg Sotzing of the University of Connecticut in Storrs, are longer and more flexible than other conductive polymers, which are short and brittle.
"You want them to be long in length to twist them together to make thread or yarn," said Sotzing.
But it's the rigidity of the chemical structure that helps conductive polymers carry a charge in the first place. Until now, that stiff structure has limited how such polymers can be processed into fibers and other useful materials.
Sotzing and his team devised a two-step method to convert flexible, non-conductive "precursor polymers" into long, conductive fibers.
The first step is to melt or dissolve the precursor polymer into a gooey solution. The researchers then apply a voltage to a special syringe and squeeze the solution through it. This process doesn't charge the polymer, but helps evaporate solvents. As a result, the polymers harden and become tangled together like the strands of a rope.
Polymers extruded by the new method can be lengthened up to three feet and potentially much longer.
At first, the fibers appear white. If the researchers dip them into a chemical solution that removes electrons, the fibers become conductive and darken to a deep blue. If the researchers apply an electric charge to add electrons, the color changes to bright orange.
"For a long time, people have known about electrochromic polymers, but they haven't figured out how to put them into formats that are useable and practical," said Shawn Williams, vice president of technology at Pittsburgh-based Plextronics, which develops conductive polymer technology for electronic devices.
What Sotzing has done, said Williams, is create a conductive polymer with the versatile properties of a regular polymer.
The trick for making the fibers useful for color-changing fabrics, according to Williams, is to control the fibers on the scale of a single pixel.
Differently charged threads could be woven together with thin metal wires designed to deliver various voltages, with the intersection between a thread and a wire serving as a pixel.
Changing the voltage with an embedded battery would result in different colors.
A fabric woven with the polymer fibers could be used, for example, in t-shirts bearing video advertisements or jackets that double as computers. The material could also be used by soldiers to blend into both forested and urban environments.
Sotzing told Discovery News that he is currently speaking to both a U.S. and foreign company about commercialization.
