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Research explores printing without chemicals

By Ian Dillingham, Daily Staff Reporter
Published February 3, 2013

In the near future, print media technology may not produce products that appear very different than what we’re used to, but under the surface there could be major improvements thanks to a new form of color production developed by University researchers.

The technology, known in the scientific community as “physical color,” allows for the production of color images without any ink, dyes or chemicals of any kind.

Jay Guo, electrical engineering and computer science professor and head of the research lab, said the innovation holds the potential to drastically change the way images are printed. Instead of coating a material with ink or chemicals, his lab uses precisely inscribed grooves to yield an observable color.

“Rather than using these chemicals, you could basically emboss the structure — a very ‘green’ print technology,” Guo said.

Not only would printed products be more environmentally friendly, they would also not be as prone to fading that occurs with current coloring techniques.

“(Current print companies are) using huge amounts of chemicals,” he said. “A press company is not exactly the greenest place … In the future, this can all be done using structural color and it would be long lasting.”

Unlike traditional color, which is produced when molecules absorb light, this new process, called “structural color,” is the result of nanocavities trapping light at specific wavelengths that depend on the cavities’ depths.

Most importantly, the cavities themselves have no chemically imposed color. Their structure alone allows them to display color to an observer.

“By making a structure rather than using these molecules, it’s purely a physical effect,” said Guo.

This same phenomenon can be seen in nature, such as the colors in the feathers of peacocks and the wings of some species of butterflies, Guo said.

By varying the depth of the cavity, the researchers can create many different colors. Because each depth corresponds to a different observable color, Guo referred to this as a “selective property.”

The cavities are manufactured through an extremely precise nano-imprint technique in the lab.

“We cannot even see these (nano-cavities) with an ordinary microscope because (the size) is beyond the diffraction limit,” Guo said.

Guo’s lab has been working on similar technology for several years. However, previous attempts have been “angle dependent,” meaning that the observable color would change based on the viewing angle. This new development has almost completely alleviated this problem, allowing the image to be viewed at any angle without changing color.

In addition to green printing, this technology has potential applications in anti-counterfeiting efforts because of the property that makes it difficult to replicate.

“These structures are really tiny … and extremely hard to reproduce,” Guo said. “In addition, you can only see this kind of structure when the electrical field is perpendicular to the grating … That kind of property is much more difficult to reproduce.”

The lab looks forward to applications in the development of a colored e-book, similar to a Kindle, which would have an extremely low power usage.

“If you make these sub-pixels colored — and control them on and off — you could get a reflective e-book,” Guo said. “If it can stay on and doesn’t consume much power, that’s what the original e-book was aiming for. The stand power could be a month.”

Rackham student Yi-Kuei Wu has worked extensively with Guo on the project. Current discussions with industry suggest that this technology will come to market in the near future, he said.

“Traditional LCD is struggling with some of the issues of (current) color filters,” Wu said. “I worked with Samsung Electronics to get a lot of practical ideas … We are trying to push this pretty hard with Samsung.”

Samsung and other companies stand to make major improvements to their current technology through implementation of physical color, Wu said. Current color filters account for 30 percent of the cost of device production, not to mention a large portion of the energy usage.

“Samsung wants to get involved in every part of the fabrication,” Wu said. “They want this technology to be transferred to their company so they can make this device themselves.”

Rackham student Cheng Zhang made major contributions to the work, particularly toward fabricating a sample image to demonstrate the viability of the technology. This project provided a unique opportunity to see the results of a new technology in daily life, he said.

“We are pushing towards some real applications,” Zhang said. “(We fabricated) five different colors in a single sample … three of them are the basic colors for reflective color filters.”

Zhang said this project has shown him how scientific discoveries can be utilized outside the lab.

“We always talk about academics … but how can we really use it?” Zhang said. “I didn’t really see it in my daily life. From this project, I know (the applications) … We have the chance to make something that has never existed before.”


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