Luminescent gel could detect stresses in mechanical systems

Researchers at MIT have developed materials that can emit light of precisely controlled colours and whose output can be tuned to respond to a variety of external conditions. The materials could be used in detecting chemical and biological compounds, or mechanical and thermal conditions.

The material, a metallic polymer gel made using rare-earth elements, is an example of work with biologically inspired materials, assistant professor of materials science and engineering Niels Holten-Andersen explained: "My niche is biomimetics - using nature's tricks to design bio-inspired polymers.”

Studying such natural materials, evolved over millions of years to adapt to challenging environmental conditions, allowed Holten-Andersen to derive design principles that can be applied to other kinds of materials.

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, resulted in a material that produces tunable, multicoloured light emissions. The light emission can then reflect subtle changes in the environment, providing a colour-coded output that reveals details of those conditions.

"It's super-sensitive to external parameters," Holten-Andersen said. "Whatever you do will change the bond dynamics, which will change the colour."

So, for example, the materials could be engineered to detect specific pollutants, toxins, or pathogens, with the results instantly visible through colour emission.

The materials are also said to detect mechanical changes, and could be used to detect stresses in mechanical systems. For example, it's difficult to measure forces in fluids but, Holten-Andersen says this 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.

Metal-coordination bonds in polymers have been the subject of other work by Holten-Andersen: In a separate paper, he reported making polymers with tunable mechanical properties, including stiffness. These materials are naturally self-assembling and self-healing and could be useful as energy-absorbing materials or in biological implants that need to be able to absorb impacts without breaking.

Author
Tom Austin-Morgan

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