Ellen Phiddian
A team of Japanese researchers has made extremely lightweight, non-fading inks in a rainbow of colours – in the same way as animal colouration.
The invention could dramatically lower the weight of paints required for big objects.
The silicon inks use “structural colour”, a form of colouration that doesn’t depend on pigments or dyes.
Structural colours come from light waves bouncing off nanometre-sized structures inside a substance. Creatures like beetles, birds and butterflies have structural colour to thank for their iridescent hues.
Unlike pigments, which create colour by absorbing some light and reflecting the rest, structural colour doesn’t fade over time.
But structural colour usually changes depending on the angle at which it’s viewed, and it’s also usually very reliant on the physical structure of the substance it’s in – such as carefully stacked crystals. This makes structural colours hard to print industrially.
These inks, described in ACS Applied Nano Materials, can be printed, and they don’t change their hue depending on angle.
They’re made by producing “nanospheres” of silicon, each about a tenth the size of a small bacterium.
“A single layer of sparsely distributed silicon nanoparticles with a thickness of only 100-200 nanometres shows bright colours but weighs less than half a gram per square metre,” says co-author Dr Hiroshi Sugimoto, a materials engineer at Kobe University.
“This makes our silicon nanospheres one of the lightest colour coats in the world.”
The nanoparticles use a phenomenon called “Mie resonance”, where spheres that are similar in size to a wavelength of light reflect that light very strongly, to deliver their colour.
The researchers are developing their inks further with the hope of commercialising them.
“We can apply it to the coating of, for example, airplanes,” says Sugimoto.
“The pigments and coatings on an airplane have a weight of several hundreds of kilograms. If we use our nanosphere-based ink, we might be able to reduce the weight to less than 10% of that.”
