This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: "Color coatings are expected to provide vivid color, brightness, gloss and long-term durability, yet no existing technology satisfies all of these requirements simultaneously," says Kobe University materials engineer Hiroshi Sugimoto. Conventional coatings usually rely on relatively thick pigment layers that fade and add significant weight.
While structural color, like that found in peacocks, isn't subject to the photofading that affects organic pigments, it does require precise alignment and changes color depending on the viewing angle. In addition, such structural arrays are incompatible with protective layers. Sugimoto has previously developed silicon nanospheres as a completely new approach to structural color, which creates angle-independent coloration, and more recently, his group achieved inkjet printing for this technology.
However, so far, reflectance has been diffuse, meaning that the surfaces lacked luster, but the trick that enabled inkjet printing opened up a path to the solution. Sugimoto explains, "Packing the nanospheres in silica shells not only protects the particles but also controls their spacing and should improve self-assembly into neat arrays." This should reduce diffuse reflectance, making the color glossy. In a paper published in the journal Small Structures, his team demonstrates glossiness and control over it while applying the coating to large 3D surfaces.
In addition, they showed that adding a protective coating did not significantly change the hue. "The most exciting aspect of this work is that it demonstrates glossy, noniridescent and protective-coated structural color coatings for 3D objects in a single platform, making the technology useful for real-world applications," explains Sugimoto. The coatings are exceptionally light, with high opacity and brightness achieved by just a single layer of silicon nanospheres.
If this were applied to wide-body airliners, it would reduce the weight of their coatings, which currently add several hundred kilograms, to several hundred grams—less than a pack of milk for the whole plane. The nanoparticles are made from silicon, a nontoxic material that can be sourced from the semiconductor industry, and silica, one of the most abundant materials in Earth's crust. Combined with their nonfading nature, color coatings might become much less resource-demanding in the future.
Sugimoto is involved in setting up a company to scale up production for industrial use. Thinking about the breadth of possible applications, he explains, "The process is compatible with scalable coating methods such as spray coating, slot-die coating and roll-to-roll processing." But Sugimoto is also a scientist, and his outlook goes beyond color coatings. He says, "We want to expand the possible applications of the science behind our technology beyond coloration.
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