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News in Brief Sensors // US Researchers Create Thin-Film Polymer Metamaterial © Based on Material by Rice University, USA

Materials scientists at Rice University and the Massachusetts Institute of Technology (MIT) have created very thin color-changing films that may serve as part of inexpensive sensors for food spoilage or security, multiband optical elements in laser-driven systems and even as part of high-contrast displays. The new work led by Rice materials scientist Ned Thomas.

The micron-thick material called a photonic gel is so inexpensive to make that, Thomas said, "We could cover an area the size of a football field with this film for about a hundred dollars." But for practical applications, much smaller pieces would do.

"Suppose you want a food sensor," said Thomas, the William and Stephanie Sick Dean of Rice’s George R. Brown School of Engineering and former chair of the Department of Materials Science and Engineering at MIT. "If it’s inside a sealed package and the environment in that package changes because of contamination or aging or exposure to temperature, an inspector would see that sensor change from blue to red and know immediately the food is spoiled."

Such visual cues are good, he said, "especially when you need to look at a lot of them. And you can read these sensors with low tech, either with your own eyes or a spectrophotometer to scan things." The films are made of nanoscale layers of hydrophobic polystyrene and hydrophilic poly(2-vinyl pyridine).

Image: Alternating, nano-sized layers of hydrophilic and hydrophobic molecules self-assemble into a block copolymer called a photonic gel, developed at Rice University and the Massachusetts Institute of Technology. It changes color depending on the amount of water absorbed by the hydrophilic layers, which can be tuned by the solvent used. © Thomas Lab/Rice University 

 

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