Conductive polymer

History

  See An Overview of the First Half-Century of Molecular Electronics by Noel S. Hush, Ann. N.Y. Acad. Sci. 1006: 1–20 (2003)

In 1963, Australians DE Weiss and coworkers reported ^[1] high conductivity in oxidized iodine-doped polypyrrole, a polyacetylene derivative. They achieved the quite low resistivity of 1.0 ohm-cm. In a series of detailed papers, they also described the effects of doping with iodine on conductivity, the conductivity type (n or p), and electron spin resonance studies on polypyrrole. The same authors noted an Australia patent application (5246/61, June 5, 1961) for conducting polypyrrole. In 1965 ^{[2] [3]}, the Australian group reached resistances as low as .03 ohm/cm with other conductive polymers. This is roughly equivalent to present-day efforts. This extensive work was "lost" until recently. E.g., Diaz et al.^[4] are often wrongly credited with discovering conductive polypyrrole in 1979.

In an "active" solid-state device, a current or voltage controls current flow. In 1974, as a "proof of concept" for their version of the now-accepted model of conduction in such materials, negative differential resistance, now a well-characterized hallmark of electronically-active organic materials. Though in a major journal and (e.g.) the subject of a contemporary news article ^[6] in the journal Nature, this work was also "lost" until similar devices emerged decades later.

It is unclear if the Nobel committee in awarding the 2000 Nobel prize in chemistry considered these earlier works. See Nobel Prize controversies.

Nobel Prize

On a similar foundations of Weiss' et al's earlier work with polypyrrole, in 1977 Shirakawa, Alan G. MacDiarmid, Alan J. Heeger and coworkers reported ^[7] high conductivity in similarly oxidized, iodine-"doped" polyacetylene. This work eventually resulted in the award to them of the 2000 Nobel prize in Chemistry. According to the citation, this was "For the discovery and development of conductive polymers" ^[8].

Chemistry

Common classes of organic conductive polymers include polyaniline. Some fungal melanins are pure polyacetylene.

Doping

In silicon semiconductors, a few of the silicon atoms are replaced by electron rich (e.g., electrolyte) to enter the polymer in the form of electron addition (n doping) or removal (p doping). Polymers may also be self-doped, e.g., when associated with a protonic solvent such as water or an alcohol.

The reason n doping is so much less common is that flask; therefore, although very useful, there are likely to be no commercialized n doped conductive polymers.

Electroluminesence

Electroluminescence and photoconductivity in organic compounds has been known since the early 1950's. However, the very poor conductivity of such materials limited current flow and thus light output. In contrast, the increased current flow through conductive polymers and improvements in their efficiency has led to the rapid development of practical polymer-based light emitting devices (OLEDs) and organic photovoltaic devices.

Properties

The biggest advantage of conductive polymers is their processibility. Conductive polymers are also elasticity, etc.) of plastics with the high electrical conductivities of a doped conjugated polymer.

Physics

In addition to "switching", an increase in conductivity can also be accomplished in a field effect transistor (organic FET or irradiation (originally-demonstrated in the 1960's ^[9]). Strong coupling can also occur between electrons and phonons (mechanical oscillations such as heat vibrations, particles of sound) since both are constrained to travel along the polymer backbone.

Applications of conducting polymers

Electroluminescence (light emission) in organic compounds has been known since the early 1950's, when Bernanose and coworkers first produced electroluminescence in crystalline thin films of acridine orange and quinacrine. In 1960, researchers at Dow Chemical developed AC-driven electroluminescent cells using doping.In some cases, similar OLEDs, solar panels and optical amplifiers.

Biological applications

Conductive polymers such as DOPA Melanin.

Current Research

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The European Union is currently funding a pan-European project into the development of conductive Polymers. The Polycondproject involves a consortium of trade associations and SME's from across Europe and is due for completion in January 2009. The main aim for this project is to develop conductive polymer products that have embedded and improved Electromagnetic Interference (EMI) and Electrostatic Discharge (ESD) protection. Research is now at an advanced stage and prototypes of products have been produced and are now being taken through a rigorous testing process to assess the Polymers performance and characterize it.

See also

• Organic semiconductor
• Molecular electronics

• "An Overview of the First Half-Century of Molecular Electronics" by Noel S. Hush, Ann. N.Y. Acad. Sci. 1006: 1–20 (2003).
• Electronic Conduction in Polymers. III. Electronic Properties of Polypyrrole BA Bolto, R McNeill and DE Weiss , Australian Journal of Chemistry 16(6) 1090 - 1103.

• Australian Journal of Chemistry, 1963 16: 1056-89
• Polycond Project

References

1. ^ http://www.drproctor.com/os/weiss.htm
2. ^ http://www.publish.csiro.au/nid/51/paper/CH9650477.htm
3. ^ http://www.publish.csiro.au/nid/51/paper/CH9650487.htm
4. ^ http://www.rsc.org/delivery/_ArticleLinking/DisplayArticleForFree.cfm?doi=C39790000635&JournalCode=C3
5. ^ http://www.drproctor.com/os/amorphous.htm
6. ^ http://www.drproctor.com/os/naturea.htm
7. ^ http://www.rsc.org/Publishing/Journals/C3/article.asp?doi=C39770000578
8. ^ http://nobelprize.org/nobel_prizes/chemistry/laureates/2000/index.html
9. ^ http://www.drproctor.com/os/photoconductivity.htm
10. ^ http://www.organicsemiconductors.com/