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Color-Changing Clothes Could Match Mood, Surroundings

John Roach
for National Geographic News
April 11, 2006
 
Next-generation threads may soon give a whole new meaning to the phrase "change your clothes"—advanced new fibers that can change color with a flip of a switch.

The threads may one day be used to make clothing that suits the wearer's mood or to allow a person to blend in with the environment.

The concept is similar to the way light-sensitive eyeglass lenses darken when exposed to sunlight.

The threads, created from materials known as electrochromic polymers, change color in response to an electric current, said Gregory Sotzing, a professor of polymer and organic chemistry at the University of Connecticut in Storrs.

"The part we're getting into is the wearable display, a flexible fabric display," Sotzing said.

An article on the research appears in the April 9 issue of New Scientist magazine.

The threads work because the polymer absorbs light across a range of visible wavelengths (related photos: the power of light).

When voltage is applied, the polymer's electrons are raised to a higher energy level. In this state the fibers absorb light of different wavelengths, and the color changes.

"You can tune color by tuning the chemistry," Sotzing said.

Flexible Fibers

Electrochromic polymers have been made before, Sotzing said. But the polymers are very rigid and can't be spun into fibers using conventional means.

"In order to spin a fiber, what you need is high viscosity [of the polymer]," he said.

"You need polymers to entangle with each other, and that's hard to do with a rigid polymer."

Trying to get a rigid material to spin into a thread, he explained, is like trying to twist together strands of uncooked spaghetti.

Researchers tried pressing electrochromic polymers into thin cylinders, but the fibers they created using this technique were rigid and extremely short—about 0.004 inch (0.01 centimeter) long.

Sotzing and his colleagues therefore developed a method to add electrochromic properties to conventional flexible polymers after they have been spun.

A regular polymer, such as nylon, is spun into a thin thread up to 0.62 mile (1 kilometer) long. As it emerges from the spinner, the scientists add groups of carbon and sulfur atoms to the thread.

The atom groups are like balls dangling from the strand. Applying an oxidant to the "decorated" threads causes the chemicals to react in such a way that the thread becomes electrochromic.

"When the balls are connected together, that's your electrochromic material," Sotzing said.

The process, he adds, can produce threads at any size—from nanoscale to conventional-size threads used in clothing.

Chameleon Clothes?

To date, Sotzing and his colleagues have developed fibers that can go from orange to blue and from red to blue. Eventually Sotzing aims to conquer the entire spectrum of visible color.

In theory these fibers and a small number of thin metal wires could be woven together in a crisscross pattern that resembles pixels.

A small battery and controller attached to the wires could then change the electric field around each pixel of fiber, changing the colors to create a pattern that matches the wearer's environment.

Right now, Sotzing said, "we don't have a t-shirt that changes color."

But ultimately he hopes to secure funding to weave the threads into a "fabric that can breathe—have air go in and out while the thing is changing color."

Manuel Marquez is an adjunct professor of bioengineering at Arizona State University in Tempe. He collaborated with Sotzing on developing this technology.

Marquez sees the fibers as having applications for flexible displays, such as computer screens, that don't become distorted when pressed.

"It's a way potentially to have a display you can bend literally and still get lifelike quality, nondistorted images," he said.

In addition to changing color when electricity is applied, Marquez says, the polymers can also change color in response to changes in the environment.

The fibers therefore could be used as sensors in the food and security industries.

For example, packaging could change color when an internal sensor detects rotten or contaminated food, he said.

Or the sensors could change color when the fibers detect harmful chemicals in the air.

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