Researchers report that they have developed polymers that can better mimic nature's colour-changing abilities than existing polymers.
Albertus P. H. J. Schenning and Monali Moirangthem, writing in the ACS Applied Materials & Interfaces journal, say the materials could enable smart decorations, camouflage textiles and improved anti-counterfeiting measures.
Most colours that people are familiar with, such as hues on a piece of paper, are made with pigments. Structural colour is another colour that is produced by periodically arranged microscopic structures that interfere with visible light.
For example, peacock tail feathers are brown, but microscopic structures present in the feathers make them look blue and green to the naked eye.
Cholesteric liquid-crystalline (CLC) polymers can easily be made into responsive materials, which is why scientists have previously used them to mimic the structural colouration found in nature.
Researchers have however, before now, only produced CLC polymers in a limited range of colours.
By using inkjet printing technology and a calcium nitrate solution to print an image on a CLC polymer they developed, Schenning and Moirangthem say they have achieved the full visible spectrum of colours.
They say printing successive layers changed the degree of swelling of the CLC polymer, changing the colour.
One layer resulted in an orange colour, a second layer changed it to green, and a third layer made it blue. As an example, the researchers used the method to draw a blue flower with green leaves on a reddish-orange background.
Once the ink dried, the image was no longer visible and the entire surface appeared blue. However, sprinkling water or breathing on it will cause the full colour image to re-appear.