Metallic gels produce tunable light emission properties
The materials could find a variety of uses in detecting chemical and biological compounds, or mechanical and thermal conditions.
The material, a metallic polymer gel made using rare-earth elements, is described in a paper in the Journal of the American Chemical Society by assistant professor of materials science and engineering Niels Holten-Andersen, postdoc Pangkuan Chen, and graduate students Qiaochu Li and Scott Grindy.
The material, a light-emitting lanthanide metallogel, can be chemically tuned to emit light in response to chemical, mechanical, or thermal stimuli – potentially providing a visible output to indicate the presence of a particular substance or condition.
The material is an example of work with biologically inspired materials.
“My niche is biomimetics – using nature’s tricks to design bio-inspired polymers,” he says. There are an amazing variety of “really funky” organisms in the oceans, he says, adding: “We’ve barely scratched the surface of trying to understand how they’re put together, from a chemical and mechanical standpoint,” explained Holten-Andersen.
Studying such natural materials, evolved over millions of years to adapt to challenging environmental conditions, “allows us as engineers to derive design principles” that can be applied to other kinds of materials.
Holten-Andersen’s own research has examined a particular kind of crosslinking in the threads mussels use to anchor themselves to rocks, called metal-coordination bonds. These bonds, he adds, also play an important role in many biological functions, such as binding oxygen to hemoglobin in red blood cells.
Holten-Andersen emphasizes that the idea is not to copy nature, but to understand and apply some of the underlying principles of natural materials; in some cases, these principles can be applied in materials that are simpler in structure and easier to produce than their natural counterparts.
In this case, the use of a metal from the lanthanide group, also known as rare-earth elements, combined with a widely used polymer called polyethylene glycol, or PEG, results in a material that produces tunable, multicolored light emissions. The light emission can then reflect very subtle changes in the environment, providing a color-coded output that reveals details of those conditions.
“It’s super-sensitive to external parameters,” said Holten-Andersen. “Whatever you do will change the bond dynamics, which will change the color.”
So, for example, the materials could be engineered to detect specific pollutants, toxins, or pathogens, with the results instantly visible just through color emission.
The materials can also detect mechanical changes, and could be used to detect stresses in mechanical systems. For example, it is difficult to measure forces in fluids, explained Holten-Andersen, but the approach could provide a sensitive means of doing so.
The material can be made in a gel, a thin film, or a coating that could be applied to structures, potentially indicating the development of a failure before it happens.
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