THE rings left behind by spilled coffee have inspired a new way to make ultrathin coatings for LCD and plasma flat-screens.
In LCDs, transparent conductive coatings are used to form an electrode on the surface of the screen, while in plasma TVs they provide a shield that prevents electromagnetic fields from straying. The traditional techniques for making such coatings include sputtering a fine layer of indium tin oxide onto the surface. ITO is highly conductive and transparent to visible light, but the process is expensive, requiring clean rooms and vacuum chambers.
Ivan Vakarelski at the Institute of Chemical and Engineering Sciences in Singapore realised that coffee stains could point the way to a cheaper alternative. Spill coffee and the evaporating liquid drives coffee particles to the edges of the spill - which ultimately produces the circular stain. The coffee granules are being "assembled" by the varying evaporation and convection rates in the fluid. Vakarelski and his colleagues figured that if they could mimic the process in a controlled fashion, they could create a pattern of granules of other materials to form a nanoscale conductive coating.