Rainbows Without Pigments Offer New Defense Against Fraud
Scientists from the University of Sheffield have developed pigment-free, intensely colored polymer materials, which could provide new, anti-counterfeit devices on passports or banknotes due to their difficulty to copy.
The polymers do not use pigments but instead exhibit intense color due to their structure, similar to the way nature creates color for beetle shells and butterfly wings.
These colors were created by highly ordered polymer layers, which the researchers produced using block copoylmers (an alloy of two different polymers). By mixing block copolymers together, the researchers were able to create any color in the rainbow from two non-colored solutions.
This type of polymer then automatically organizes itself into a layered structure, causing optical effects similar to opals. The color also changes depending on the viewing angle. This system has huge advantage in terms of cost, processing and color selection compared to existing systems.
The complexity of the chemistry involved in making the polymer means they are very difficult for fraudsters to copy, making them ideally suited for use on passports or banknotes.
The academics used Diamond Light Source, the UK’s national synchrotron science facility in Oxfordshire, to probe the ordered, layered structures using high power X-rays. This helped them understand how the colors were formed, and how to improve the appearance.
Dr Andrew Parnell, from the University of Sheffield’s Department of Physics and Astronomy, said: “Our aim was to mimic the wonderful and funky colored patterns found in nature, such as Peacock feathers. We now have a painter’s palette of colors that we can choose from using just two polymers to do this. We think that these materials have huge potential to be used commercially.”
Professor Nick Terrill, Principal Beamline Scientist for I22, the Diamond laboratory used for the experiment, explained: “Small Angle X-ray Scattering is a simple technique that in this case has provided valuable confirmatory information. By using Diamond’s X-rays to confirm the structure of the polymer, the group was able to identify the appropriate blends for the colors required, meaning they can now tailor the polymer composition accordingly.”
Image 1: The polymer materials can be made into robust layers that could be used as anti-counterfeit measures on banknotes. Credit: University of Sheffield
Image 2: This multicolored image shows the range of colors that can be made by mixing the two block copolymers in varying proportions. Credit: University of Sheffield
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