Chameleon-like security aid
The chameleon’s ability to change the colour of its skin makes it a fascinating example of how to adapt to the environment. Their colour-changing ability is made possible by many layers of cells which can reflect light. Changing the chemical structure of these cells changes the colour of the reflected light. Scientists at the University of Sheffield have come up with a way to replicate this phenomenon in the lab and can see some very useful applications for it such as in combating counterfeit crime.

Inspired by nature
The main driver for their research initially was working on light filters for windows to stop buildings heating up.  Dr Andrew Parnell, who leads the research from the University of Sheffield's Department of Physics and Astronomy explains, ‘If you look in nature at butterfly wings and beetle shells they use structural colour rather than dyes and pigments. They use layers of one material and another material which have different optical properties and are able to manipulate light.’

Compared to previous processes that were expensive and complicated, the team found that polymers want to form this structure. Because it self assembles the material is cheap to manufacture. ‘This is because the polymers don’t like to mix,’ as Parnell says, ‘just like oil and water don’t like to mix. We get these layered structures with very good high quality interfaces between the layers and that’s what gives us these really nice optical effects.’

Diamond Light Source, in Oxford, provided the very powerful x-ray source they needed to measure the structures and see at a nano level the optical properties of the structures of the polymers they were using. In July they will be using the synchrotron in France to develop further their understanding of how the polymers structures behave.

Commercial application
They’ve had a good level of interest and have patented their work in the UK and around the world. Parnell can see colour-changing polymers being used commercially, ‘on your passport or your bank note to give people confidence that the document is real. It is the sort of material that people can check by themselves they don’t need a florescent light to look at it people can be sure that their ten dollars or ten rupees is not a forgery.’