Scientists get charged up over trying to electrify plastic
Sliding his arms into neoprene gloves that reach inside a glass tank of pure nitrogen, the researcher picks up a thin film that looks like aluminum foil but is actually a plastic polymer.Skip to next paragraph
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''It doesn't look like your average Handiwrap,'' says Gary Wnek, an assistant professor of polymer science at MIT, standing nearby.
The researcher places the strip in a test tube, sloshes it with a green chemical, and watches it turn sooty, like a fireplace grate.
''That will now conduct electricity,'' proclaims Mr. Wnek of the material.
What the two men have done in a few seconds in an MIT lab is alter what has been the conventional wisdom about plastics for more than a century: that they don't conduct electricity and, in fact, are among the best known insulators.
Scientists have been turning this convention on its head in similar experiments for almost a decade. But the trick has been to come up with a practical ''synthetic metal'' for use outside the lab.
Now they are getting tantalizingly close - and the result could, at last, open the way for the electric car and affect everything from the batteries in your videocassette recorder to the development of new solar cells.
On the surface, any attempt to electrify plastic would seem superfluous. There are, after all, plenty of metals around that carry current fine. But what excites many scientists is the potential for polymers to perform a few electrical tricks that metals can't - while at the same time costing little and weighing even less.
The groundwork for many of today's developments in the field was laid through a bit of serendipity. In 1975, while on a visit to Japan, Alan MacDiarmid, a chemist at the University of Pennsylvania (Penn), sat down over tea with Hideki Shirakawa, a Japanese scientist.
The Japanese professor chatted about an unusual new polymer (a plastic consisting of a long chain of molecules) that looked more metallic than plastic. The material itself was the result of a botched lab experiment by one of Mr. Shirakawa's students. Intrigued, MacDiarmid invited Shirakawa to Penn to probe the possibilities of the substance - work that later led to ''doping'' it with a solution (iodine) that produced a current-carrying polymer.
Today interest in the field is robust, but the problems that remain in hatching a commercial conducting polymer are formidable. Some 20 scientific papers are being published each month on the subject. By conservative estimates the US alone. Chemists from large companies such as Xerox, IBM, and Allied Corporation are among those searching for ways to move them from lab bench to marketplace. ''The field seems to have caught on very rapidly,'' MacDiarmid says.
The best conducting polymers that exist now in the lab remain about 100 times less conductive than copper. But this isn't the real drawback with the ''synmetals.'' A chief snag is that they are chemically unstable in air and water. This is why the experiment in the MIT lab is carried out in a nitrogen tank. There is also the difficulty of processing the materials. With most plastics, you either melt or dissolve the material, then slap it in a mold, and out pops a product. Many conducting polymers are headstrong and antisocial: They won't dissolve or melt.
Scientists, though, are making some progress at trying to turn this class of materials into less of a commercial misfit. One approach: Find an entirely new polymer. Alan MacDiarmid and colleagues at Penn, for instance, recently came up with a form of polyaniline, a polymer that has been around in various forms for 100 years, which may lead to rechargeable batteries containing water instead of organic solvents. Water solutions are better conductors and are nontoxic.
In the lab, Penn researchers have converted a standard flashlight battery into a rechargeable cell. They claim their conducting polymer could be manufactured cheaply and handled easily in the lab.
Another tack is to find a non-conduct-ing material that can be easily processed, then make it a current carrier later. A lot of effort, too, is going into testing composites of various polymers - matching one, say, that conducts well with one that is air-stable.
None of this chemical wizardry, however, is likely to yield new products soon. Widespread commercial applications probably won't come before the late 1980s and '90s.
''They hold a lot of promise - but a lot of work has to be done yet, too,'' cautions Dr. Louis Hillenbrand, a senior scientist at Battelle Columbus Laboratories.
When they do emerge, plastic metals are expected to show up in batteries first. Prototypes have been recharged hundreds of times without wearing out. The lightweight cells also promise to have higher power and energy densities than most conventional batteries - and can be molded to fit in tight spots (a car door, for example).
They could also help revive the electric automobile: A key drawback to these vehicles has been the weight and short charge-time of conventional batteries.
Other applications range from use by utilities in storing excess power, to diodes in computer chips, to solar cells that convert sunlight directly into electricity.
As with any new material, though, what excites many scientists is the unknown. His feet propped up on a table mounded with plastic models of molecules , Wnek peers out the window of his MIT office at a leaden sky. ''I'm not saying conducting polymers are going to revolutionize'' the world, he says, but the ''limitations that were on the blackboard just four years ago are no longer there.''