Sheffield, England--Polymer alloys mixed by researchers at the University of Sheffield rely on a resulting photonic structure (rather than pigments) to create intense colors, and as a result can be made into sophisticated anti-fraud materials for passports and other essential documents, and maybe even paper money.1
The material is unusual because it is not only difficult to fabricate without the proper setup, but is straightforward to make at low cost with the right materials (and the right equipment). The colors, which are tunable during manufacture between 400 to 850 nm, arise from the the photonic structure, similar to the way nature creates color for beetle shells and butterfly wings (thus the “biomimetic” label).
The colors are created by highly ordered polymer layers that the researchers make using block copolymers (an alloy of two different polymers). The two polymers, which differ from each other in molecular weight, separately have no color, but when blended and shear-aligned, form the color-tailorable structure. The complexity of the chemistry involved in making the polymer means they are very difficult for counterfeiters to copy.
The academics used the Diamond Light Source (Oxfordshire, England), the United Kingdom’s national synchrotron science facility, to probe the ordered structures using high-power x-rays. This helped them understand how the colours were formed, and how to improve the appearance.
"Small angle s-ray scattering is a simple technique that in this case has provided valuable confirmatory information,” said Nick Terrill, principal beamline scientist for I22, the Diamond laboratory used for the experiment. “By using Diamond's x-rays to confirm the structure of the polymer, the group was able to identify the appropriate blends for the colours required, meaning they can now tailor the polymer composition accordingly."
The institutions involved in the research include the University of Sheffield, the University of Hull, and Diamond Light Source in Oxfordshire.
For more information, contact Shemina Davis, Media Relations Officer, at [email protected]
REFERENCE:
1. Andrew J. Parnell et al., Soft Matter 7, p. 3721 (2011). DOI: 10.1039/C0SM01320J
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