The new great wave

June 19, 2019

Katsushika Hokusai (1760 - 1849) is the Titan of Japanese art, as revered in his homeland as Da Vinci, Van Gogh, and Rembrandt Van Rijn are in the West. Of all his famed masterpieces the 'Great Wave' stands out as the ultimate testament to his artistic genius.

Now, a team of researchers at Kyoto University has created the smallest 'Great Wave' ever produced, just 1mm in width. What's more they have managed something that even Master Hokusai couldn't do. They've created it without the use of pigments.

The human condition demands that we create art. Some 38,000 years before Hokusai picked up his woodblocks and kogatana knives, an inhabitant of the Lubang Jeriji Saléh cave in East Kalimantan, Borneo, Indonesia created the world's first-known figurative painting when she/he drew a picture of a bull on the wall using ochre. Artists ever since, from the Upper Paleolithic Era to 1800s Japan to the street artists of today, have all shared a common dependency: the need for pigments.

Until now, that is. Not only is the 'Great Wave' created at Kyoto University the world's smallest, it is also the first ever printed without use of a pigment. Professor Easan Sivaniah, head of the Pureosity Group at iCeMS, Kyoto University, where the research was developed, explains.

"Polymers when exposed to stress - a kind of 'stretching out' at molecular level - undergo a process called 'crazing' in which they form tiny, slender fibers known as fibrils," he explains. "These fibers cause a powerful visual effect. Crazing is what the bored school kid sees when he repeatedly bends a transparent ruler until the stretched plastic starts to cloud into a kind of opaque white".

Significantly, the iCeMS researchers realized that by controlling the way the microscopic fibrils were formed and organized in a periodic pattern, a process called Organized Microfibrillation (OM), they can also control this scattering of light to create colors across the whole visible spectra, from blue to red. Thus a new revolutionary new palette is born. Printing need no longer depend on pigment.

Zoologists have long been familiar with this non-pigment-based color phenomenon, which they term 'structural color'. It is exactly how nature produces the vivid colors seen in butterfly wings, the spectacular plumage of male peacocks, and other shimmering, iridescent birds. Some of the most spectacular wildlife on the planet is, in fact, devoid of pigmentation and depends upon light interacting with the surface structure for its mesmerizingly beautiful effect.

The OM technology allows an inkless, large-scale color printing process that generates images at resolutions of up to 14000 dpi on a number of flexible and transparent formats. This has countless applications, for example, in anti-forgery technology for banknotes. But as Sivaniah is at pains to emphasize, its applications go way beyond conventional printing ideas.

"OM allows us to print porous networks for gases and liquids, making it both breathable and wearable. So, for example in the area of health and well-being, it is possible to incorporate it into a kind of flexible 'fluid circuit board' that could sit on your skin, or your contact lenses, to transmit essential biomedical information to the Cloud or directly to your health care professional".

OM is flexible technology in both the literal and figurative sense. The Kyoto University researchers have proved the technology works in many commonly used polymers, such as polystyrene and polycarbonate. The latter is a widely used plastic in food and medicine packaging, so there is clearly an application in food and drug safety, where security labels can be created much like a watermark to ensure a product has not been opened or sabotaged.

Masateru Ito, lead author of the paper, published this month in Nature, thinks there is more to come from the basic principles raised by this groundbreaking research. "We have shown that stress can be controlled at the submicron length scales to create controlled structure," he notes. "However it may be that it can also create controlled functionality. We demonstrated it in polymers, and we also know that metals or ceramics can crack. It is exciting to know if we can similarly manipulate cracks in these materials too.
Keywords: Organized Microfibrillation (OM); printing; inkless printing; material science; color; structural color; anti-forgery; health; wellbeing; food; medicine.

Kyoto University

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