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Conductive polymer

 

Conductive polymer

Chemical structures of some conductive polymers. From top left clockwise: polyacetylene; polyphenylene vinylene; polypyrrole (X = NH) and polythiophene (X = S); and polyaniline (X = NH/N) and polyphenylene sulfide (X = S).

Conductive polymers or, more precisely, intrinsically conducting polymers (ICPs) are

  • Conducting Polymers for Carbon Electronics – a Chem Soc Rev themed issue with a foreword from Alan Heeger

External links

  • Hyungsub Choi and Cyrus C.M. Mody The Long History of Molecular Electronics Social Studies of Science, vol 39.
  • F. L. Carter, R. E. Siatkowski and H. Wohltjen (eds.), Molecular Electronic Devices, 229-244, North Holland, Amsterdam, 1988.

Further reading

  1. ^
  2. ^ a b c d
  3. ^ a b Handbook of Nanostructured Materials and Nanotechnology; Nalwa, H.S., Ed.; Academic Press: New York, NY, USA, 2000; Volume 5, pp. 501–575.
  4. ^ a b
  5. ^
  6. ^ Y. Okamoto and W. Brenner Organic Semiconductors, Rheinhold (1964)
  7. ^
  8. ^
  9. ^
  10. ^ B.A. Bolto, R. McNeill and D.E. Weiss "Electronic Conduction in Polymers. III. Electronic Properties of Polypyrrole" Australian Journal of Chemistry 16(6) 1090, 1963.
  11. ^ Organic Semiconductors by Yoshikuko Okamoto and Walter Brenner, Reinhold (1964). Chapt.7, Polymers, pp125-158
  12. ^
  13. ^
  14. ^
  15. ^
  16. ^ a b
  17. ^
  18. ^
  19. ^ Heeger, A. J., Nature of the primary photo-excitations in poly(arylene-vinylenes): Bound neutral excitons or charged polaron pairs, in Primary photoexcitations in conjugated polymers: Molecular excitons versus semiconductor band model, Sariciftci, N. S., Ed., World Scientific, Singapore, 1997. Handbook of Organic Conductive Molecules and Polymers; Vol. 1–4, edited by H.S. Nalwa (John Wiley & Sons Ltd., Chichester, 1997).
  20. ^ Handbook of Conducting Polymers; Vol.1,2, edited by T.A. Skotheim, R.L. Elsenbaumer, and J.R. Reynolds (Marcel Dekker, Inc., New York, 1998). Semiconducting Polymers; Vol., edited by G. Hadziioannou and P.F.v. Hutten (Wiley-VCH, Weinheim, 2007)
  21. ^
  22. ^
  23. ^
  24. ^ Skotheim, T., Elsenbaumer, R., Reynolds, J., Eds.; Handbook of Conducting Polymers, 2nd ed.; Marcel Dekker, Inc.: New York, NY, USA, 1998
  25. ^
  26. ^
  27. ^
  28. ^ The Future of ITO: Transparent Conductor and ITO Replacement Markets
  29. ^ Handbook of Nanostructured Materials and Nanotechnology; Nalwa, H.S., Ed.; Academic Press: New York, NY, USA, 2000; Volume 5, p. 501
  30. ^ Overview on Organic Electronics
  31. ^ Organic Electronics Association
  32. ^ Conjugated Polymers: Electronic Conductors (April 2001)

References

See also

[32] Most recent emphasis is on organic light emitting diodes and organic

Trends

Experimental and theoretical thermodynamical evidence suggests that conductive polymers may even be completely and principally insoluble so that they can only be processed by dispersion.[29]

Since most conductive polymers require oxidative doping, the properties of the resulting state are crucial. Such materials are salt-like (polymer salt), which diminishes their solubility in organic solvents and water and hence their processability. Furthermore, the charged organic backbone is often unstable towards atmospheric moisture. The poor processability for many polymers requires the introduction of solubilizing or substituents, which can further complicate the synthesis.

Barriers to applications

solar panels, and optical amplifiers.

Electroluminescence

With the availability of stable and reproducible dispersions, PEDOT and polyaniline have gained some large scale applications. While PEDOT (poly(3,4-ethylenedioxythiophene)) is mainly used in antistatic applications and as a transparent conductive layer in form of PEDOT:PSS dispersions (PSS=polystyrene sulfonic acid), polyaniline is widely used for printed circuit board manufacturing – in the final finish, for protecting copper from corrosion and preventing its solderability.[3]

Due to their poor processability, conductive polymers have few large-scale applications. They have promise in antistatic materials[2] and they have been incorporated into commercial displays and batteries, but there have had limitations due to the manufacturing costs, material inconsistencies, toxicity, poor solubility in solvents, and inability to directly melt process. Literature suggests they are also promising in actuators, electrochromism, supercapacitors, chemical sensors and biosensors,[27] flexible transparent displays, electromagnetic shielding and possibly replacement for the popular transparent conductor indium tin oxide.[28] Another use is for microwave-absorbent coatings, particularly radar-absorptive coatings on stealth aircraft. Conducting polymers are rapidly gaining attraction in new applications with increasingly processable materials with better electrical and physical properties and lower costs. The new nanostructured forms of conducting polymers particularly, augment this field with their higher surface area and better dispersability.

Properties and applications

Despite intensive research, the relationship between morphology, chain structure and conductivity is still poorly understood.[24] Generally, it is assumed that conductivity should be higher for the higher degree of crystallinity and better alignment of the chains, however this could not be confirmed for polyaniline and was only recently confirmed for PEDOT,[25][26] which are largely amorphous.

Undoped conjugated polymers state are semiconductors or insulators. In such compounds, the energy gap can be > 2 eV, which is too great for thermally activated conduction. Therefore, undoped conjugated polymers, such as polythiophenes, OFET) and by irradiation. Some materials also exhibit negative differential resistance and voltage-controlled "switching" analogous to that seen in inorganic amorphous semiconductors.

Although typically "doping" conductive polymers involves oxidizing or reducing the material, conductive organic polymers associated with a protic solvent may also be "self-doped."

The conductivity of such polymers is the result of several processes. For example, in traditional polymers such as phosphorus, or electron-poor, e.g., boron, atoms to create n-type and p-type semiconductors, respectively.

Molecular basis of electrical conductivity

The low solubility of most polymers presents challenges. Some researchers have addressed this through the formation of nanostructures and surfactant-stabilized conducting polymer dispersions in water. These include polyaniline nanofibers and PEDOT:PSS. These materials have lower molecular weights than that of some materials previously explored in the literature. However, in some cases, the molecular weight need not be high to achieve the desired properties.

n H–[X]–H → H–[X]n–H + 2(n–1) H+ + 2(n–1) e

Conductive polymers are prepared by many methods. Most conductive polymers are prepared by oxidative coupling of monocyclic precursors. Such reactions entail dehydrogenation:

Synthesis

The main chain contains Heteroatoms present
No heteroatom Nitrogen-containing Sulfur-containing
Aromatic cycles The N is in the aromatic cycle:

The N is outside the aromatic cycle:

The S is in the aromatic cycle:

The S is outside the aromatic cycle:

Double bonds
Aromatic cycles and double bonds

The following table presents some organic conductive polymers according to their composition. The well-studied classes are written in bold and the less well studied ones are in italic.

The linear-backbone "polymer blacks" (solar cells and transistors.[2]

Types

[17][16] While mostly operating in the

In 1963 Australians B.A. Bolto, D.E. Weiss, and coworkers reported derivatives of semiconductors. Subsequently, DeSurville and coworkers reported high conductivity in a polyaniline.[12] Likewise, in 1980, Diaz and Logan reported films of polyaniline that can serve as electrodes.[13]

The first highly-conductive organic compounds were the superconductivity[9] following the discovery of BCS theory.

Polyaniline was first described in the mid-19th century by Henry Letheby, who investigated the electrochemical and chemical oxidation products of aniline in acidic media. He noted that reduced form was colourless but the oxidized forms were deep blue.[4]

History

Contents

  • History 1
  • Types 2
  • Synthesis 3
  • Molecular basis of electrical conductivity 4
  • Properties and applications 5
    • Electroluminescence 5.1
    • Barriers to applications 5.2
    • Trends 5.3
  • See also 6
  • References 7
  • Further reading 8
  • External links 9

[3] and by advanced dispersion techniques.[2]

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