Researchers in Japan have developed a lightweight, non-shimmering structural color ink.

Materials engineers at Kobe University have succeeded in developing a suspension of silicon nanoparticles to create a non-shimmering and lightweight textured colored paint. This new way of creating color uses the scattering of light of a specific length around small, almost perfectly round silicon crystals. This achievement from Kobe University makes it possible to print structural colors that are independent of viewing angle and do not fade. The material has low environmental and biological impact and can be applied in very thin layers, promising significant weight savings compared to conventional paints.

An object has a color when light of a certain wavelength is reflected. In traditional pigments, this occurs when molecules absorb white light from other colors, but over time this interaction causes the molecules to break down and the color to fade. Structural colors, on the other hand, typically arise when light bounces off parallel nanostructures placed just the right distance apart so that only light of certain wavelengths survives, while others are neutralized, reflecting only the color we see. This phenomenon can be observed on the wings of butterflies or the feathers of peacocks and has the advantage that the colors are not degraded. But from an industrial perspective, the carefully arranged nanostructures cannot be easily colored or printed, and the color depends on viewing angle, making the material iridescent.

Kobe University materials engineers Fuji Minoru and Sugimoto Hiroshi have developed a completely new approach to flower production. They explain: In previous work starting in 2020, we were the first to achieve precise particle size control and obtain colloidal suspensions of spherical and crystalline silicon nanoparticles. These individual silicon nanoparticles scatter light to create vibrant colors through the phenomenon of “Mie resonance,” allowing us to develop structured color inks. In Mie resonance, spherical particles comparable in size to the wavelength of light reflect specific wavelengths with particular intensity. This means that the color returned by the suspension can be controlled simply by changing the particle size.

In their work, published in the journal ACS Applied Nano Materials, Fujii and Sugimoto demonstrate that the suspension can be applied to surfaces and thus coat the base material in a structural color manner that is independent of viewing angle. This is because color is created not by the interaction of light reflected from adjacent structures, as is the case with “traditional” structural colors, but by highly efficient scattering around individual nanospheres. Sugimoto explains another advantage: a single layer of sparsely distributed silicon nanoparticles, just 100-200 nanometers thick, displays vibrant colors but weighs less than half a gram per square meter. Thanks to this, our silicon nanospheres have one of the lightest color layers in the world.

After further development and refinement of their technology, interesting applications await. Sugimoto explains: We can apply it to aircraft skins, for example. Pigments and coatings on an airplane weigh several hundred kilograms. If we use our nanosphere-based inks, we can reduce the weight to less than 10%.