Polymer films promise high-tech windows, advertising, other products

May 9, 2001

GAINESVILLE, Fla. — Windows that change from transparent to opaque at the touch of a button — and greeting cards that display flashing messages — may not be far in the future, thanks to research at a University of Florida chemistry lab.

UF chemistry Professor John Reynolds and his research group have created a new family of “electrochromic polymer” films that are capable of displaying a wide variety of colors, including green, orange, blue and purple. Once perfected, the polymer films, which can be incorporated into devices both thinner than a credit card and flexible, could change the color of any surface. To adjust to bright light, they could darken windowpanes like built-in shades — even adorn packages or cards with flashing display ads or personal messages.

“I think in general we’re going to see active devices made with these kinds of materials in many commercial products quite soon,” Reynolds said.

Researchers have been investigating electroactive and conducting polymers for more than two decades, with the three pioneers of the field receiving last year’s Nobel Prize for chemistry. At UF, the Reynolds group has focused on the electrochomic effect, or the process by which molecules change color when subjected to an electric current. Through its research, the group has increased the number of colors the polymers can display — along with boosting the speed at which they switch from a clear state to a colored state.

The technology is similar to that used in some new cars’ rearview mirrors that sense bright lights and darken automatically, Reynolds said. The mirrors consist of two pieces of conducting glass, between which is a gel that contains electrochomic molecules. When approaching headlights hit a light sensor in the mirror, it switches on an electric current, causing the molecules to darken and the mirror to reduce glare for the driver.

The UF research uses polymer films directly attached to the conducting glass to replace the electrochromic molecules in the gel. Sandwiched between two plates of glass, they can turn a variety of colors based on the molecular structure of the polymers as conceived and engineered in Reynolds’ lab. Unlike the mirror, however, which darkens in approximately five seconds, the polymer films change color within a half second or less.

Conducting polymer films with a similar composition are already used by a major company as part of the manufacturing process for photographic film as well as in printed circuit boards for computers and solid-state capacitors. But Reynolds said the potential applications for the polymers is broad, and he predicted a host of applications in the future, ranging from multicolored cell phone displays to chemical and biological sensors. He is also working with UF professors Kirk Schanze, Jim Boncella and Paul Holloway to develop materials that can emit light outside the visible spectrum, including near-infrared light. Such materials might be useful in fiber optic telecommunications, he said.

Reynolds has published more than 150 papers in a broad array of scientific journals about his research. Most recently, he co-authored a paper that appeared in this month’s issue of the journal “Advanced Materials” along with collaborating professor David Tanner and graduate students Irina Schwendeman, Jungseek Hwang and Dean Welsh. The paper discusses using high-contrast electrochromic polymer films as one way to control the amount of reflection from a metal surface.

Reynolds’ research group consists of 18 scientists, including 12 graduate students who are studying various aspects of organic polymer and materials chemistry. The research has received funding from numerous federal agencies, including the National Science Foundation and various Department of Defense agencies, and a variety of companies.