ALL THAT GLITTERS
About 15 minutes before this photo was taken, these droplets—mixtures of latex and gold nanoparticles in water—were all just a cloudy red. But as the water evaporated, a mosaic of colors appeared in each, a result of a phenomenon called structural color. Unlike color generated from dyes, which absorb and transmit certain colors of light, structural color like this comes from the arrangement of nanometer-size particles. As the droplets shrank due to evaporation, the latex particles were squeezed together into a crystalline structure. Depending on the spacing of the particles in that structure, which depended on the diameter of the latex spheres, different wavelengths of light were amplified in certain places in the droplet, resulting in the range of colors shown. The gold nanoparticles do not themselves significantly change the colors produced. Instead they increase the contrast between colors.
Credit: Courtesy of Orlin Velev