Every once in a while I'll see a plastics-related technology story that seems so amazing that it's almost hard to believe. That's the case with this Science Daily story on tiny self-propelled polystyrene balls that can navigate narrow channels -- like a human blood stream. Researchers coated one side of each PS ball with a thin layer of platinum, then dropped them into a solution of hydrogen peroxide and water.
This metal catalyzes a reaction in which hydrogen peroxide breaks into oxygen and water. Because the reaction spits out three molecules for every two that it consumes, the polystyrene ball is pushed from the platinum side. Objects as small as these polystyrene balls naturally wander about randomly, a phenomenon caused by jostling about among vibrating atoms and molecules. This "random walk" movement is called Brownian motion. To account for it, the platinum-coated balls were tested against polystyrene balls with no coating. Over short distances, they found that the half-coated balls moved in a particular direction although their paths meandered over longer distances. Still, the wanderings of the coated balls were distinct from the Brownian motion of the uncoated balls. Their paths were a random walk with step sizes that depended on the concentration of hydrogen peroxide. The larger the hydrogen peroxide concentration, the larger the step.They don't seem to have an application for this phenomenon yet, but with all the research into nanotechnology, I can imagine that these jet-propelled little balls could have an interesting future.