In a report recently published in Nature Communications, a research group led by Associate Professor Joel Yang from the Singapore University of Technology and Design (SUTD) printed probably the smallest colorful 3-D model of the Eiffel Tower. Impressively, no pigments or inks were used. Instead, the 3-D-printed model of the Eiffel Tower, measuring less than half the width of a human hair at 39 micrometers, exhibits multiple colors due to the manner in which light interacts with the nanostructures that hold up the model. The 3-D models are made of a finely printed mesh of transparent polymer, forming photonic crystals. These mostly hollow designs remarkably shrink down in size by about 5 times when heated to produce a wide range of colors.
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Source: Phys.org