True blues

From plant protection to advertising and electronics, polymers are here to stay

 
Published: Sunday 15 February 1998

polymers that turn ultraviolet (uv) light into visible light could be used for everything from advertising to protecting plants from damage as the ozone layer thins. Researcher Rudi Danz from the Fraunhofer Institute for Applied Polymer Research in Teltow, usa, has developed polymers that contain napthalene groups, which excited by incoming uv radiation at wavelengths between 200 and 380 nanomatres, absorb the light and re-emit the energy as visible blue light. Danz says that the polymers could be turned into plastic sheeting or applied as a coating on glass.

One use would be in displays. A sign coated with one of the scintillating polymers would glow bright blue whenever illuminated by an invisible beam of uv light . Similarly, these polymers could also be used as warning indicators. "In labs or factories with uv radiation hazards, these polymers could provide a visible indication of this invisible, ionising radiation," says Danz.

It may also be desirable to cover greenhouses with the polymers as more uv radiation gets through the ailing ozone layer. "Plants can use some uv light, but too much of it is harmful," says Danz.

In another develpment, Genovation of Thirsk in New York, usa, has perfected a family of stretchy polymers that could be used to make a new generation of slimmer, effective and more efficient medical sensors, keyboards and other medical and electronic equipment. These polymers do not conduct electricity unless vibrated, twisted or squeezed. The company is already working on a medical tape which will monitor heartbeat and breathing rate once it is stuck to the subject's chest. Also on the drawing boards are an all-plastic keyboard and a torch that gets brighter the harder it is squeezed.

Because the material stops conducting electricity once an upper threshold of current is reached, it can also be used as a resettable fuse.

As patents on these elastomers are still being granted, Genovation is still somewhat reluctant to give away the details. Andrew King, head of product development, will only say that the properties of these elastomers depend on both the blend of chemicals in the material as well as the physical arrangement of the atoms. While the most delicate versions react to sound vibrations, the stiffest need a good jab of the finger to turn them into conductors.

However, these materials suffer from one disadvantage. Under constant load, the current in the material rises gradually until a peak is reached. But once the pressure is released, the elastomers return to their original insulating state. Genovation scientists claim that the conducting properties of these elastomers persist even after they have been squeezed and twisted over 250,000 times. (New Scientist , Vol 156, No 2112).

Subscribe to Weekly Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.