Zhejiang University scientists invent programmable plastics to achieve invisible storage of information

Professor Xie Tao of Zhejiang University proposed a method of accurate "coding" in plastic products, by digitally regulating the internal "stress" of plastic products, implanting delicate "stealth" patterns, and realizing the invisible storage of information. The paper was published online in the journal Nature Communications.Zhang Guogao, the first author of the
paper and a doctoral student at Zhejiang University, showed reporters several coin-sized transparent plastic sheets, which clearly showed patterns
National
) such as QR codes, colored butterflies, and Mona Lisa portraits under polarizing lenses.
"We didn't add pigments to the material, we didn't change the microstructure of the surface of the material, there were patterns because of stress," he said. Zhang Guogao said that stress is brought in by process reasons, in plastic products is an inevitable ubiquity, will be later released in the form of warping, deformation, and even cracking, which is one of the reasons why plastic products are not durable.
due to stress, the refractive index in all directions inside the transparent material is different. Under polarization lenses, the interior of the plastic exhibits a colorful color.
team found a digital control stress method. The researchers first evenly stretched a polymer plastic film at about 60 degrees Celsius to store stress, and then used a laser printer to print different grayscale patterns on the polymer film and irradiated it with infrared light to "eliminate" stress on a plain negative. Temperature differences make each pixel stress release different, so the stress takes on a fine gradient change. In this way, the pattern is "transcoded" from grayscaness to stress distribution, and a preset "invisible" pattern is formed in the material.
" in materials, stress is usually a passively introduced, uncontrollable factor. And we control this force, 'code' operation, to produce more functions. Xie Tao says the first visible application is the invisible storage of information. Only with the help of polarization lenses can we see the patterns stored in the material. Zhang
, a researcher, believes that stress is related to the optical properties, electrical properties and structure of materials. By "coding" stresses, programmable plastics will show more functionality. "For example, now that all 3D printing is from liquid materials to solids, our approach offers a possibility from solids to solids."
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