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Zhejiang University scientists invented programmable plastic

the research group of Professor Xie Tao of Zhejiang University proposed a method of accurate "coding" in plastic products, which can digitally adjust and control the internal "stress" of plastic products, implant exquisite "invisible" patterns, and realize the invisible storage of information. Relevant papers were published in the journal Nature communications a few days ago

Zhang Guogao, the first author of the paper and a doctoral student of Zhejiang University, showed several pieces of transparent plastic in the size of coins. 2. The operation method of the concrete pressure testing machine. Under the polarizing lens, these transparent plastic sheets clearly showed two-dimensional codes, colorful butterflies, Mona Lisa portraits and other patterns

"we didn't clean the dust and other impurities in the electrical box before the tensile testing machine was powered on, add pigments to the materials, and didn't change the microstructure of the material surface. The pattern was due to stress." Zhang Guogao said that stress is brought in by process reasons, which is inevitable and widespread in plastic products, and will be released in the form of warpage, deformation, and even cracking in the future, which is also one of the reasons why plastic products are not durable

because of the existence of stress, the refractive index in all directions inside the transparent material is different. Under the polarized lens, the interior of plastic products will show colorful colors

the research group has found a method to digitally control stress. The researchers first stretched a polymer plastic film evenly at about 60 degrees Celsius to store the stress, and then printed different gray patterns on the polymer film with a laser printer, irradiated with infrared light, and "eliminated" the stress at a fixed point on the plain negative. The difference of temperature makes the stress release degree of each pixel different, so the stress shows a fine gradient change. In this way, the pattern is "transcoded" from grayscale to stress distribution, and then a preset "invisible" pattern is formed in the material

"in materials, stress is usually a passively introduced and uncontrollable factor. We control this force and carry out 'coding' operation to produce more functions." Xie Tao said that the first visible application is to realize the invisible storage of information. "Only with the help of polarized lenses can we see the pattern of material storage."

Zhang Guogao believes that stress is related to the optical properties, electrical properties and structure of materials. By "coding" stress, programmable plastics will show more function. "For example, now all 3D printing is from liquid, but the unit of a is g material to solid. Our method provides a possibility from solid to solid."

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