Coloured polymer coatings could help prevent fraud

The coating has a highly complex structure based on bespoke combinations of block co-polymers (essentially alloys of two different polymers), making it extremely difficult to forge.

Nevertheless, project lead Dr Andrew Parnell from Sheffield University said that now they understand the phenomenon in detail, it should be easy and cheap to scale up for things such as banknotes and passports.

Their transparent coating creates colour through the optical transmission of certain wavelengths of light — rather than simply reflecting light with metallic-coloured ink, which is currently used in some banknotes.

Comparing the existing technology with their method, Parnell said: ’For a specific colour you have to make a specific-sized particle, such as a sphere, and in order to make another colour you have to make an entirely new material — so from our point of view we can mix and match quite easily.’

They do this by combining co-polymers of differing molecular weights then ’shear aligning’ them using a curing process to form a unique optical structure.