A rainbow-colored grating, about 25 millimeters wide, under sunlight. Enlarged microscope images show the graded surface, with the black bars indicating a length of 10 microns. Image: University at Buffalo |
University at Buffalo
engineers have developed a one-step, low-cost method to fabricate a polymer
with extraordinary properties: When viewed from a single perspective, the
polymer is rainbow colored, reflecting many different wavelengths of light.
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,” said UB Vice President for Research and Economic Development
Alexander N. Cartwright, one of the UB researchers who led the study.
The ease of producing the polymer could make it feasible to
develop small devices that connect with cell phones to conduct multispectral
imaging, said Qiaoqiang Gan, a UB 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 said.
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. (It’s the same principle that gives color to the
wings of butterflies and feather of peacocks.)
Cartwright and Gan’s team reported on their polymer fabrication
technique online in Advanced Materials.
Coauthors on the study also include UB students Ke Liu and Huina Xu and UB
research scientist Haifeng Hu.
The UB Office of Science, Technology Transfer and Economic
Outreach (STOR) has submitted a provisional patent application detailing the
production process to the U.S. Patent and Trademark Office.
To create the rainbow material, Liu and Xu 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 mm 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 said 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.
