"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 shortabout 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 sizefrom nanoscale to conventional-size threads used in clothing.
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 breathehave 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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