PLASTIC FINDS ITS PULLING POWER

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PLASTIC FINDS ITS PULLING POWER
25 August 2004 - New Scientist

THE world's first plastic magnet to work at room temperature has passed the elementary test of magnetism. Its creators at the University of Durham in the UK have used it to pick up iron filings from a laboratory bench. In 2001, chemists from the University of Nebraska-Lincoln claimed to have created the world's first plastic magnet, but it only worked below 10 kelvin. Other researchers have made plastic magnets, but typically they only function at extremely low temperatures, or their magnetism at room temperature is too feeble to be of commercial use. So the Durham team can claim to have made the first plastic magnet that could be used in everyday products.

One of the most likely applications is in the magnetic coating of computer hard discs, which could lead to a new generation of high-capacity discs. Jerry Torrance, a materials scientist based in California who is a consultant to some of the world's largest electronics and engineering companies, including IBM, describes the work as 'a significant scientific breakthrough'. However, he says that practical applications are probably still a long way off.

The new polymer was developed by Naveed Zaidi and his colleagues in Durham's organic electroactive materials group. The team created the new polymer from two compounds, emeraldine base polyaniline (PANi) and tetracyanoquinodimethane (TCNQ). They chose PANi because it is a metal-like electrical conductor that is stable in air. TCNQ was chosen because of its propensity to form charged particles called free radicals. In conventional magnets, magnetism is the result of electron spins lining up. In their polymer, the researchers hoped to mimic this mechanism by creating an alignment of free radicals.

At first the new polymer showed little sign of magnetism, and after three months the researchers had reached the point where they felt that trying to induce magnetism in this polymer was a waste of time. 'Just as we were about to give up and try a different approach, we decided to check the samples for a last time,' says Sean Giblin.

It was a fortunate decision, because over the months the original polymer had developed magnetic properties. Further batches of the polymer confirmed its magnetism and ruled out the possibility that the magnetism had been caused by contamination. In addition, X-ray diffraction data showed an increase in the alignment of the polymer chains over three months, which probably accounts for the increase in magnetism.

Although the polymer's magnetism is weak compared with conventional metal magnets, the researchers are confident that they can improve it. 'The reaction is not yet 100 per cent efficient along the polymer and the strength of effect varies throughout the material. Once we increase this efficiency, this overall strength will certainly increase,' says Zaidi.

The nature of polymer synthesis means that magnetic properties could effectively be made to measure, by varying the proportions of the initial chemicals. 'This is only the beginning. From this initial polymer, much better systems can be synthesised in future,' says Zaidi.

And in addition to computer hard discs, the team thinks that plastic magnets could have important medical applications, for example in dentistry or the transducers used in cochlear implants. Organic magnetic materials are less likely to be rejected by the body.

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