What makes something red, or blue, or green? It’s all in the way light bounces off its surface. Something that primarily reflects light with shorter wavelengths will appear bluer, while something that reflects longer wavelengths will appear redder. By playing around with that principle, scientists have created a material that, much like soap bubbles and certain insect wings, displays a gorgeous iridescence – a shifting rainbow of colours they can tweak with the same surface.
The film, and a microscopic image of the film. Image: ICMAB
Even more interestingly, the researchers made this material from common cellulose, the simple stuff that makes up paper and which can be extracted from wood, cotton or other renewable sources. We’ve already mentioned scientists arranging cellulose fibres in a way that makes them appear incredibly white. But now instead of laying fibres, a team of physicists are moulding cellulose films with tiny, regularly-spaced impressions (like an upside-down LEGO piece).
The outcome was a thin, single-centimetre iridescent film that reflects light based on the spacing of the dots, according to the paper published recently in Nature Photonics.
Etching surfaces like this isn’t a new trick. But the researchers behind this project are especially excited about using a stamp or a mould to pattern the cellulose, since it’s so easy, cheap and reproducible, they write. And cellulose can be put on top of metals, washed, eaten, and many other things, which means we could be seeing a lot more of these shimmering rainbows.
This is just a single paper about a single lab’s work, so I’m not going to tell you that in the next two years, pills, foods and electronics will be coloured with nanoprinted dots instead of dyes and paints. But that would be pretty cool.