ADVANCED MATERIALS & PROCESSES | SEPTEMBER 2023 1 1 MATERIAL MOVES MATTER In Japan, a group of researchers from the RIKEN Center for Emergent Matter Science developed a unique composite material that acts in a non- reciprocal way. Based on nanofillers embedded in a hydrogel, the material can channel mechanical energy in one direction but not the other. The team was able to use vibrational up-anddown movements with their composite material to make liquid droplets rise within a material against gravity. Using this material could thus make it possible to make use of random vibrations and move matter in a preferred direction. To create this uniform and scalable material, scientists took a hydrogel and embedded graphene oxide nanofillers into it at a tilted angle. The hydrogel was fixed to the floor, so that the top part could move when subjected to a shear force, but not the bottom. When shear force is applied from right to left into the leaning nanofillers, they tend to buckle and hence lose their resistance. But if the force comes from the other direction, and the nanofillers are facing away from it, the applied shear merely makes them stretch even longer and they’re able to maintain their strength. This allows the sheet to deform in one direction but not the other. The group measured this difference, finding that the material was approximately 60 times as resistant in one direction than the other. According to the researchers, their next goal is to find applications for the material and use it to make effective use of vibrational energy, which up until now has been seen as waste. www.riken.jp/en. LENS MATERIAL FOR SELF-DRIVING CARS Researchers at the Korea Research Institute of Chemical Technology (KRICT) and Kyungpook National University, both in South Korea, developed a material that can heal scratches on the sensor of an autonomous vehicle within 60 seconds. According to the team, they were able to activate the self-healing properties by using a simple tool—such as a magnifying glass—to irradiate focused sunlight. EMERGING TECHNOLOGY Scientists at the DOE’s Oak Ridge National Laboratory, Tenn., invented a coating made of carbon nanotubes that could dramatically reduce friction in load-bearing systems with moving parts, from vehicle drivetrains to wind turbines. The researchers say it reduces the friction of steel on steel by at least a factor of 100. ornl.gov. BRIEF Self-healing mechanism of lens material for self-driving cars utilizing sunlight, a dynamic polymer network, and photothermal dye. Courtesy of KRICT. Schematic depicting the preparation of a composite hydrogel with unidirectionally aligned graphene oxide nanosheets. Courtesy of Science (2023), DOI: 10.1126/ science.adf1206. Because self-healing is favorable when molecular movement within the polymer is free, flexible materials are generally used by scientists to ensure high performance. However, lenses and protective coating materials are made of hard materials, and thus challenging to activate the self-healing function. To solve this problem, the researchers combined a thiourethane structure and a transparent photothermal dye to design a dynamic chemical bond in which the polymers repeat both disassembly and recombination under irradiation of sunlight. The team’s material shows optimized self-healing performance, even when scratches cross each other, and maintains 100% of the self- healing efficiency even if the process of scratching and healing at the same location is repeated more than five times. www.krict.re.kr/eng/, en.knu.ac.kr/ main/main.htm.
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