1999 WINNER 16-19 YEARS

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By Elizabeth Tasker The future's bright, the future's plastic MR Brown finished his work for the evening and shut the computer down. He rolled up the monitor and tucked it safely away as the office darkened. His windows were adjusting their colour to preserve the heat inside the house, as the sun set. He tiptoed upstairs and stuck his head round his son's door. The soft glow from the wallpaper provided the perfect night light for him to see that his son was sleeping peacefully. Next door, his daughter had completed her school project. She could print out designs from her computer that lit up when connected to a battery. Perched on the top of her desk, a television screen the size of a thumbnail was displaying a late night film. With microsized televisions, flexible computer screens, windows that change colour, illuminated wallpaper and luminous signs you can print yourself, this house of the future has it all. But how far fetched is this plastic technology? Surprisingly, the answer may be ''not very''. So far our flexible friend has been used for applications as diverse as chairs and credit cards but is perhaps not the first substance that springs to mind when considering electrical components. That is, until now. Until quite recently, plastics were considered insulators - substances, which are unable to conduct electricity. The discovery that this was not always the case was made in the 1970s by Hideki Shirakawa, now at the University of Tsukuba in Japan, when his student made a mistake while concocting a polymer. His error led to the birth of plastic electronics. Polymers are the constituents of our household plastics consisting of a small organic molecule, where many copies are repeatedly linked to form a long chain. Scientists discovered that if they took these polymers and added other atoms, the mixture became electrically conductive. This process, called doping, typically removes conducting electrons, leaving a polymer with some positive charges. With fewer electrons, those that remain in the polymer can move more freely, allowing conduction. Electrical conductivity is not the only application of conjugated polymers. Certain materials can change their properties -such as transparency -when voltage is applied. A plastic that can be darkened electrically could be used to darken windows on hot days and made transparent when the weather is colder. And these polymers can emit light. Scientists, notably Prof Richard Friend of Cambridge, sandwiched a film of semiconducting polymer between a transparent positive electrode and a negative electrode. The latter electrode injects electrons into the film, while the positive electrode pulls them out - a process equivalent to injecting positively charged ''holes.'' On the polymer chains, the electrons and holes form charged species called polarons. These migrate until polarons of opposite charge meet and combine to form an exciton (an excited state of the polymer). In some cases these excitons recombine -decay - to give off light. Today's top-of-the-range flat screens, such as those on lap-top computers, form an image from millions of pixels (picture elements). Unfortunately, it only takes a few pixels to malfunction for the image to be ruined. This makes the reject rate of such screens high and bumps up the price. The new conducting plastic display screens could solve this problem as they are easier to make, especially when large, and are less sensitive to impurities. More excitingly, a new type of flexible display should make it possible to roll up a screen and carry it under your arm, as you would a newspaper. And the plastics could be deposited as inks, allowing incredibly thin screens to be produced. Such inks could be dispersed via a printer to allow you to design your own circuit, luminous design or even wallpaper on your computer. Once printed, it could be plugged in to light up instantly. If that is not enough to assure you that these plastics are the way to the future, other uses are found in the military where a ''stealth'' conducting plastic has been designed to fool radar, making the plane impossible to detect. So when can we expect to see these products on the market? Perhaps even this Christmas, predicts Dr Andy Monkman of Durham University. ''International companies have already set up pilot factories for these products,'' he says. ''There should be something by the end of this year.'' With so much imagination and enthusiasm behind these plastics, Mr Brown and his house of the future are closer to reality than ever. BACK