|
TEXT ONE William Illiam Morris suggested that nothing should have a place that is not known to be useful or believed to be beautiful. Opals, though, might be both. A group of researchers from the University of Southampton, in England, and the German Plastics Institute in Darmstadt, led by Jeremy Baumberg, have discovered how to create a plastic with the gemstones iridescent properties. Their invention could be used to make a sparkling substitute for paint, banknotes that are hard to counterfeit and chemical sensors that can act as visible sell-by dates. Opals get their milky sheen and rainbow sparkle from the way light is scattered by the tiny crystals that form them. These crystals are stacked in what is known as a face-centred cubic structure. This means that the constituent atoms are arranged in a lattice of cubes, with one extra atom sitting at the centre of each cubes six faces. Light entering this lattice gets bounced around in ways that generate colour by reinforcing the peaks of some wavelengths and cancelling out those of others. For many years researchers have been trying to develop a synthetic material with the same light-scattering properties as an opal, by etching patterns into various materials. That approach has failed. Instead, Dr Baumberg has built his opalescent material from scratch. He and his team grew tiny polystyrene spheres until they were some 200 nanometres across, before hardening them with a blast of heat. They then coated the spheres with a sticky polymer before heating them again. As the mixture was baked, the spheres moved naturally into a face-centred cubic structure. | 
