Luminescent Gel Changes Color to Indicate Mechanical Stresses

Chemically tunable lanthanide metallogel emits different colors depending on conditions.

A group of researchers at MIT have developed a family of metallic polymer gels made with rare earth elements that are capable of emitting controllable colored light.

Luminescent materials produced by the MIT team are shown under UV light, emitting different colors depending on their environmental conditions. (Image courtesy Tara Fadenrecht.)

Luminescent materials produced by the MIT team are shown under UV light, emitting different colors depending on their environmental conditions. (Image courtesy Tara Fadenrecht.)

The metallogel is made from lanthanide metals combined with a polyethylene glycol (PEG) polymer. The gel can be chemically tuned to emit different colored light over a wide spectrum, including white light. The light emissions are in response to chemical, biological, mechanical or thermal stimuli affecting a material compound or physical structure.

“It’s super-sensitive to external parameters,” said Niels Holten-Andersen, assistant professor at MIT. “Whatever you do will change the bond dynamics, which will change the color.”

The material can be made into a gel, a thin film, or a coating that could be applied to structures. Because it can detect stresses in mechanical systems, explained Holten-Andersen, it can potentially indicate the development of a failure before it actually happens.

It is also difficult to measure forces in fluids, Holten-Andersen said, but an approach using this metallogel could provide a sensitive means of doing so.

The metallogel can also be engineered to detect specific pollutants, toxins or pathogens and provide visible results through color-coded emissions.

MIT’s material is an example of work with biologically inspired materials, Holten-Andersen explained. “My niche is biomimetics – using nature’s tricks to design bio-inspired polymers,” he said. “We’ve barely scratched the surface of trying to understand how they’re put together, from a chemical and mechanical standpoint.”

The idea is not to copy nature, he emphasized, but to understand and apply the underlying principles of natural materials.

A paper by Holten-Anderson and his colleagues describing the metallic polymer was published in the Journal of the American Chemical Society and is available here.