Conducting Polymers Conducting Polymers

Grant OffordCH 392N

April 23, 2009

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Presentation OutlinePresentation Outline

• History and Development

• Polymer Conductivity• Doping

• Processibility• Future of Conducting

Polymers

http://www.cmeter.org/pled/index.html

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The Nobel Prize in Chemistry (2000)The Nobel Prize in Chemistry (2000)

"for the discovery and development of conductive polymers"

H. Shirakawa A. G. MacDiarmid A. J. Heeger

J. Chem. Soc. Chem. Comm. 578-580 (1977)

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Shocking ResultsShocking Results

Polyacetylene Iodine-dopedPolyacetylene

Polyacetylene conductivity increases by nearlyten orders of magnitude after iodine doping.

http://nobelprize.org/nobel_prizes/chemistry/laureates/2000/public.html

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Did they really discover it?Did they really discover it?

No! This result was obtained in 1963!

A series of three papers by D.E. Weiss were “lost,”and then Diaz was credited with the discovery of polypyrrole as a conducting polymer.

D.E. Weiss, Aust. J. of Chem. 663 1056-1103 (1963) A.F. Diaz, J. Chem. Soc. Chem. Comm. 635-636 (1979)

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What makes polymers conductive?What makes polymers conductive?

• Conducting polymers are (almost) all conjugated pi systems

• Pi electrons are delocalized

• Delocalization usually found in rigid sp2

carbon backbone

Molecular Engineering of pi-Conjugated Polymers, Adv. in Poly Sci. 145 (1999)

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What makes polymers conductive?What makes polymers conductive?

• Insulators– Filled valence band,

unfilled conduction band, large band gap

• Semiconductors– Same as insulator,

smaller band gap

• Conductors– Partially filled valence

and conduction bands, no band gap

Molecular Engineering of pi-Conjugated Polymers, Adv. in Poly Sci. 145 (1999)

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Basics of Polymer DopingBasics of Polymer Doping

• Doping can increase conductivity by a factor of 1012.

• Two kinds: oxidative (p-doping) and reductive (n-doping)

• Bipolaron Formation

http://nobelprize.org/nobel_prizes/chemistry/laureates/2000/public.html

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How is a polymer doped?How is a polymer doped?

• Chemical Doping– Expose polymer

directly to oxidant (I, Br, acid) or reductant(alkali metals)

• Electrochemical Doping– Coat electrode with

conducting polymer– Immerse in electrolyte

(not polymer soluble) with counter electrode

– Potential difference causes counterion to enter polymer

– Can occur during or post-synthesis

J. Chem. Soc. Chem. Comm. 578-580 (1977)Molecular Engineering of pi-Conjugated Polymers, Adv. in Poly Sci. 145 (1999)

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Conducting Polymer Conducting Polymer ProcessibilityProcessibility

• Conjugated Polymers– Generally insoluble

when unsubstituted

• Option one: attach flexible side groups!

Prog. Polym. Sci. 27 135-190 (2002)

• Option two: dopant-enhanced solubility– DBSA/polyaniline

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Organic LED TechnologyOrganic LED Technology

• SM-OLED– Used in current

commercial applications

– SM vacuum deposition– Glass substrate

1. Cathode (Al)

2. Emissive Layer3. Radiation Emission

4. Conducting Layer5. Anode (ITO)

Graphic courtesy of Wikipedia entry “Organic light-emitting diode”

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Organic LED TechnologyOrganic LED Technology

• PLED– Emerging technology– “Inkjet Printing”– Flexible Substrate

(PET)

Poly(3,4-ethylenedioxythiophene)(PEDOT)

Appl. Phys. Lett., Vol. 72, No. 21, 25 May 1998

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Organic PV TechnologyOrganic PV Technology

• Donor– Polymer (PEDOT)

• Acceptor– C60

• Polymer PVs– Lightweight, flexible,

inexpensive

• Many novel uses

Graphic courtesy of Wikipedia entry “Polymer solar cell”http://www.technologyreview.com/energy/21574/

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Questions?Questions?

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Contemporary UsesContemporary Uses

• Storage Batteries• Biosensors

• Displays• Mechanical Actuators

• EMI Shielding

• Conductive Textiles• Antistatic Films/Fibers

• Neutron Detection• Non-linear optics

• Electroluminescence

A wide array of applications!