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.
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