New Applications Keep Friends' Past Research In Spotlight

When physicist Alan Heeger and chemist Alan MacDiarmid were launching their careers two decades ago at the University of Pennsylvania in Philadelphia, "conducting polymer" was an oxymoron. Metals conducted electricity, plastics were lightweight and pliable, and never the twain should meet. No longer. Today, the polymer polyace-tylene's conductivity equals that of copper. The potential commercial applications of conducting polymers, such as aircraft and missile coatings, antistatic fibers, and conductive shields for electronic equipment, have sparked new interest in both the scientific and business communities. Plastic batteries are already on the market in Japan, and Lockheed Corp. of Calabasas, Calif., has announced plans for the large-scale production of polyaniline, another conducting polymer. At the same time, all that is still unknown about this class of materials offers scientists a lifetime of work. One could suggest that the world might never have known about these conductive plastics if it weren't for the friendship between Heeger and MacDiarmid at Penn in the early 1970s. This is simplistic, of course; certainly it ignores the influences of talent and perseverance. But ultimately it comes down to this: Research into conducting polymers demands that physicists and chemists work in tandem. The complexities of the material insist upon it. And the bedrock of a good interdisciplinary collaboration, according to the pair, is generosity, patience, and communication. In a word: friendship. Heeger and MacDiarmid began investigating the conductivity of polyacetylene in 1977, after a lucky accident in a Japanese laboratory revealed the material's unique potential. While trying to make polyacetylene from acetylene welding gas, a graduate student accidently added 1,000 times more catalyst than what was called for. Instead of obtaining polyacetylene in its normal dark powder form, he got a metallic-looking film that could be stretched. Subsequently, MacDiarmid and Heeger found that this form of polyacetylene could be made conductive by adding iodine to it. "We knew immediately after the discovery of conducting polymers that there was a special opportunity here," recalls Heeger. "One had the potential for materials that had the electronic and optical properties of metals and semiconductors and the processing advantages and mechanical properties of polymers. The problem was that in the early days, the `and' [pairing semiconductor and polymer properties] wasn't true." Combining the best characteristics of metals and polymers became the focus of MacDiarmid and Heeger's research, first together and then, after 1982, separately. Mac-Diarmid, a professor of chemistry, continues his research at Penn. Heeger left to found the Institute for Polymers and Organic Solids at the University of California, Santa Barbara, with synthetic chemist Fred Wudle. Although the specific challenges vary, the overall thrust of their work continues to be how to make a better conducting polymer. To study the hybrid material today requires research teams that are equally hybrid. Synthetic and physical chemists, experimental and theoretical physicists, polymer scientists, theoretical chemists, electrochemists, and electronic engineers all have found a niche in this new field. It isn't always comfortable in the scientific melting pot, however. To be successful, Heeger declares, scientists must have the ability to work on the boundaries of three fields: physics, chemistry, and polymer science. This obligates group members not only to learn several scientific vocabularies, but also to appreciate different ways of conceptualizing problems. For example, it is the tendency of the synthetic chemist to think in terms of pictures, says MacDiarmid, while the theoretical physicist thinks in terms of algebraic equations. MacDiarmid recalls one baffling conversation that he had early on with Heeger. Heeger was referring to "deep traps in the band gap" to explain why the photoconductivity of conducting polymers was not very high. The language puzzled Mac-Diarmid. "I said, `What do you mean by deep traps in the band gap?' And he [Heeger] wrote down on paper some algebraic relationships between the band gap and the charged carriers that were being absorbed and trapped. To me that did not mean anything until I, then, as a chemist, started thinking: Okay, a quantum of light comes in, and you get a positive charge left behind, and this is then a free radical species and that then wants to combine with an electron, which may be wanting to make the photoconductivity. And so that free radical then reacts with it. And that's what he meant by `deep traps in the band gap.' " Communication difficulties like these can spell doom for a collaboration. When a common language doesn't exist, when it's difficult to follow the other person's train of thought, then trust and confidence must step in and take their place, the collaborators say. "You have to believe that the other person's judgment is important," Heeger says. "If you have that kind of generosity, then it's a real collaboration, and things begin to happen." On a conducting polymer team, the work of the chemists and physicists is both independent and complementary. These two qualities can be seen in the way the field progresses according to "phases of emphasis," to use Heeger's term. One phase might require research in the realm of synthetic chemistry and the next phase might lean on experimental physics, yet ultimately each will contribute to a larger whole. "There's an initial discovery and a development of concepts and a phenomenon," Heeger says. "Then you become limited in your ability to answer questions because of the material's limitations." The burden then falls upon polymer science to improve the material, to orient it, to extend its chain length, and to strive toward the ideal situation of putting the polymer's macromolecules straight and in parallel. "Then, when you have that," Heeger says, "you can come back and explore the fundamental questions at a level you couldn't get at earlier." MacDiarmid and Heeger's early papers continue to be highly cited, evidence of both the significance of their pioneering work and the vibrancy of the field. One survey paper that appeared in Synthetic Metals ("Organic metals and semiconductors: The chemistry of polyacetylene and its derivatives," 1:101-18, 1979/1980) has been cited about 200 times since its publication. The number of scientists working with conducting polymers has increased as well. For example, at this year's International Conference on Science and Technology of Synthetic Metals in Tubingen, Germany, there were 923 registrants, up from 40 at the first such meeting in the 1970s. One reason for this strong showing is that the field has reached the point at which practical applications are beginning to be marketed. Business Week (Dec. 11, 1989, page 114) recently ran an article detailing possible uses for conducting polymers. And industry interest is high. For example, MacDiarmid and his colleague Arthur J. Epstein of Ohio State University in Columbus have a partnership with Lockheed and interact with other companies when appropriate. Earlier this year, Heeger, with UC-Santa Barbara materials scientist Paul Smith, founded UNIAX, a company dedicated to the commercial development of these polymers. Conducting polymer research has also attracted the recognition of awards committees. Last year, for example, MacDiarmid was one of the recipients of Philadelphia's John Scott Awards, given in recognition of the pioneering research he performed with Heeger. The prestigious cadre of previous winners includes Marie Curie, Louis Pasteur, Albert Einstein, and Orville and Wilbur Wright. Yet even as the field matures and these sorts of interdisciplinary collaborations become well established, the role of trust and good will remain central. Epstein, whose team at Ohio State University has collaborated with MacDiarmid's team since 1985, encourages his graduate students to contact the Penn students directly and to learn to take charge of their own working relationships. "We felt at the beginning that we could not act as gatekeepers for the students," says Epstein, who was trained as a physicist but is a professor of both physics and chemistry. "So one of the things we've strived to do is develop a relationship among our two groups where the students are comfortable in working with each other." In this partnership, the students are responsible for initiating their own arrangements with the other team, sending samples, and coordinating experiments. The fax and phone lines are constantly buzzing, and every three or four months the two groups meet at a Holiday Inn located in Somerset, Pa., a point halfway between Columbus and Philadelphia. There, over the course of a few days, each student presents his or her work. MacDiarmid and Epstein, committed to making this a conference for the students, do not present any research. Epstein recalls one Holiday Inn conference that was especially marked by good will and camaraderie: after the presentations were over, the students stayed out most of the night drinking and dancing. The van ride back to Columbus, ordinarily a rolling four-hour meeting, turned into nap time. The students were somewhat embarrassed, but Epstein thought it was great. "They might not see it yet, but I understand that building that relationship is half the battle," he says. "These guys are their friends. They're going to help them succeed, and by doing [that] they're going to succeed themselves." Liz Marshall is a freelance science writer based in Pittsburgh.

New Applications Keep Friends' Past Research In Spotlight

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