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Counterfeiting is an arms race. Governments look for tricky printing techniques, and criminals look for ways to replicate them. A group from the Korea Advanced Institute of Science and Technology thinks their Janus balls, named after the two-faced Roman god of comings and goings, would be hard for ne’er-do-wells to pull off. They used microfluidics to create tiny magnetic spheres that are colorful on one side and black on the other. Normally, density controls the color, with the heavier side of the spheres facing down. But a magnetic field makes them flip, changing the color.
Read more in ACS Nano (2020, DOI: 10.1021/acsnano.0c06672)
Credit: ACS Nano/Shin-Hyun Kim
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