Rainbow polymer reveals true colors

U. BUFFALO (US) — A new rainbow-colored polymer could lead to handheld applications for color identification.

Used as a filter for light, this material could form the basis of handheld multispectral imaging devices that identify the “true color” of objects examined.

“Such portable technology could have applications in a wide range of fields, from home improvement, like matching paint colors, to biomedical imaging, including analyzing colors in medical images to detect disease,” says Alexander N. Cartwright, professor of electrical engineering at the University at Buffalo and one of the researchers who led the study.


Because the engineers have developed a one-step, low-cost method to fabricate the polymer, it may be feasible to develop small devices that connect with cell phones to conduct multispectral imaging, says Qiaoqiang Gan, assistant professor of electrical engineering and another member of the research team.

“Our method is pretty low-cost, and because of this and the potential cell phone applications, we feel there is a huge market for improving clinical imaging in developing countries,” Gan says.

Because the colors of the rainbow filter are produced as a result of the filter’s surface geometry, and not by some kind of pigment, the colors won’t fade over time. The same principle applies to the color of butterflies’ wings and to peacock feathers.

Cartwright and Gan’s team report on their polymer fabrication technique in the journal Advanced Materials.

To create the rainbow material, students Ke Liu and Huina Xu, co-authors of the study, sandwiched a photosensitive pre-polymer syrup between two glass slides. A photosensitive substance is one whose physical properties change upon exposure to light.

Next, they directed a laser beam through a curved lens placed above the pre-polymer solution. The lens divided and bent the laser beam into light of continuously varying wavelengths.

As this light hit the solution, monomers in the solution began joining into polymers, forming a continuous pattern of ridge-like polymer structures. Larger ridges rose where the light struck with more intensity.

The resulting structure is a thin filter that is rainbow-colored when viewed under white light. This is because the periodic polymer layers reflect a continuous spectrum of colors, from red on one end to indigo on the other.

The single-step fabrication method—shining a laser light through a curved lens—is affordable and relatively simple.

The filter the researchers created was about 25 millimeters long, but the technique they used is scalable: It’s possible to create filters of different sizes by shining the laser through lenses of different sizes.

Gan says the next step for the researchers is to improve the quality of the rainbow filter. The team is also beginning to explore ideas for incorporating the technology into handheld devices.

UB has submitted a provisional patent application detailing the production process to the U.S. Patent and Trademark Office.

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