Drive and Curiosity by Hargittai Istvan

Author:Hargittai, Istvan.
Language: eng
Format: epub
Publisher: Random House Publisher Services

MacDiarmid had been at UPenn since 1955, having been born and brought up in New Zealand and having earned his first PhD at the University of Wisconsin and his second at Cambridge University, United Kingdom. He had become a respected inorganic chemist whose work received steady support from the Office of Naval Research (ONR). When he returned from his Japanese sojourn, MacDiarmid talked with his contact at ONR. It was a fruitful interaction, and he asked the ONR officer for approximately $23,000 to support Hideki Shirakawa as a postdoctoral fellow in his laboratory. The ONR man was a little reluctant, because polymer organic chemistry was not MacDiarmid's field; he was neither a polymer chemist nor an organic chemist. Nonetheless, based on the ONR's previous experience with MacDiarmid's research, his request was granted and Shirakawa arrived at UPenn in September 1976 for a one-year visit.

Shirakawa had not been particularly interested in electric conductivity of polyacetylene, and when he measured it, it did not show much conductivity anyway. The first task to which MacDiarmid and Shirakawa addressed themselves was to see whether the electric conductivity of their polyacetylene samples could be enhanced. The focus on this property was justified by the metallic appearance of the substance and by MacDiarmid's prior experience with the sulfurnitrogen polymer. As chemists like to work with pure samples, the team set themselves to purify their polyacetylene.To their surprise, the purer the sample became, the more its electric conductivity diminished. This gave them the idea of purposely making less pure samples. The procedure of contaminating on purpose is called doping; this procedure has become the distinguishing feature between conducting polymers and all other polymers.

The doping increased the electric conductivity of the polyacetylene samples ten million times! The essence of the process is that the very rigid electronic structure of alternating single bonds and double bonds in polyacetylene is loosened by the addition of a few percent of agents; for example, halogens. These attract electrons away from the chain, thus creating electron holes (the locations of the missing electrons); and these emerging electron holes are easy to transmit along the polymer chain; hence the conductivity.

MacDiarmid understood soon enough that in addition to polymer chemistry and organic chemistry, yet another domain of science was being involved in these conducting polymers—con-densedstate physics, the science of solids and liquids. He therefore invited a physicist from the excellent neighboring Physics Depart-ment of UPenn to join their quest for creating this heretofore unheard-of new field of materials.

Soon Alan Heeger, a UPenn physicist, became the third member of MacDiarmid and Shirakawa's winning team. The story of their initial contact is worth retelling because it shows that even specialists of fields as closely related as inorganic chemistry and condensed-state physics need to be concerned about speaking a common language. According to Alan Heeger, it was not long before MacDiarmid was to leave for Japan that he went to Mac-Diarmid's office and heard his description of “SNX,” a wonderful material.4 MacDiarmid told him that it had metallic properties and suggested a joint study, but Heeger was not interested.

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