Researchers from the Massachusetts Institute of Technology have developed a metallic polymer gel that can emit light of precisely controlled colours – even pure white light — and whose output can be tuned to respond to a wide variety of external conditions. The material could prove useful in detecting chemical and biological compounds, or mechanical and thermal conditions.
The MIT team has described the material in the Journal of the American Chemical Society.
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 new material is an example of work with biologically inspired materials. Studying such natural materials, which have evolved over millions of years to adapt to challenging environmental conditions, allows engineers to derive design principles that can be applied to other kinds of materials, explained Niels Holten-Anderson, assistant professor of materials science and engineering at MIT.
To produce a material that produces tunable, multi-coloured light emissions, professor Holten-Anderson and his team used a metal from the lanthanide group – also known as rare-earth elements – combined with a widely used polymer called polyethylene glycol, or PEG. The light emission can then reflect very subtle changes in the environment, providing a colour-coded output that reveals details of those conditions.
‘It’s super-sensitive to external parameters,’ noted Holten-Andersen. ‘Whatever you do will change the bond dynamics, which will change the colour.’
There are several potential applications for the invention. For example, the material could be engineered to detect specific pollutants, toxins, or pathogens, with the results instantly visible just through colour emission.
And, because the materials can also detect mechanical changes, they could be used to detect stresses in mechanical systems, Holten-Andersen said. Currently, it is difficult to measure forces in fluids, he added, but 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.
‘What’s nice here is that the materials change colour in response to such a wide and rich set of stimuli,’ commented Stephen Craig, a professor of chemistry at Duke University who was not involved in this research. ‘The fact that the reference state can be made white is quite useful; it’s often easier to detect by eye that something has a faint shade of green, for example, than that it is one shade of green as opposed to another.’