CONDUCTIVE POLYMERSPRESENTATION AT

DEPARTMENT OF CHEMISTRY KNUST

BY

KWABENA BOADU OFFEI-KORANTENG

(MPHIL POLYMER SCIENCE AND TECHNOLOGY II) 1

OUTLINEIntroductionTypes and Properties of polymersConductive polymers and examplesWhat is conductivity?What makes a material conductive?How can plastics become conductive?Conditions for conductivityApplications.Conclusion. 2

Introduction• Polymers are known to have good insulating

properties. (they are used in electrical and

electronic applications as insulators)

• Polymers are one of the most used materials in the

modern world.  Their uses and application range from

containers to clothing.

• They are used to coat metal wires to prevent electric

shocks. 3

Types of polymers• Rubber or elastomers• Plastics • Fiber

Properties of polymers

Lightness Ease of processing (spin coating)

Low cost

Strength

Flexibility

elasticity

Mouldability

ease of handling 4

Conductive polymer

• Conductive polymers are polymers

that conduct electricity.

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Example of Conducting Polymers

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n

HN

n S nNH n

Polyacetylene

(PA)

Polyaniline

(PANI)

Polythiophene

(PT)

Polypyrrole

(PPy)

n n S n

O O

Polyfluorenes

(PF)Poly(p-phenylene

vinylene)(PPV)

Poly(3,4-ethylenedioxythiophene)

(PEDOT)

nPoly(p-

phenylene)(PPP)

nPoly(p-phenylene

ethynylene)(PPE)

What is conductivity?

• Conductivity is the ability of a material to pass an electric current. In a metal the outer electrons are free to carry charge and the  impedance to flow of charge is mainly due to the electrons "bumping" in to each other. 

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What makes a material conductive?• Three simple carbon compounds are diamond, graphite and

polyacetylene.

Diamond, which contains only σ bonds, is an insulator and its high symmetry gives it isotropic properties.Graphite and acetylene both have mobile π electrons and are, when doped, highly anisotropic metallic conductors.

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How can a polymer become conductive?

• For a polymer to become electrically conductive, the polymer: has to imitate a metal, that is, its electrons need to be free to move and not bound to the atoms. Polyacetylene is the simplest possible conjugated polymer. It is obtained by polymerisation of acetylene,

9cis-polyacetylene 10–8 -10–7 S m–1

trans-polyacetylene 10–3 -10–2 S m–1

conditions for conductivethe polymer consists of alternating single and double bonds, called conjugated double bonds.

(In conjugation, the bonds between the carbon atoms are alternately single and double. Every bond contains a localised “sigma” (σ) bond which forms a strong chemical bond. In addition, every double bond also contains a less strongly localised “pi” (π) bond which is weaker).

10Molecular Engineering of pi-Conjugated Polymers, Adv. in Poly Sci. 145 (1999)

conditions for conductivePolymer has to be disturbed - either by removing electrons from (oxidation), or inserting them into (reduction), the material. (Doping; the role of the dopant is either to remove or to add electrons to the polymer.)

• There are two types of doping: oxidation with halogen

Polymer + X (polymer)n+ + Xn-

Reduction with alkali metal Polymer + M (polymer)n- + Mn+

X= I2, Br2, AsF5……. M = Na, Li………. 11

Doping process (cont…,)The iodine molecule attracts an electron from the polyacetylene chain and becomes I3

-. The polyacetylene molecule, now positively charged, is termed a radical cation, or polaron.

The lonely electron of the double bond, from which an electron was removed, can move easily. As a consequence, the double bond successively moves along the molecule. This movement of charge is what is actually responsible for electrical conductivity.

The positive charge, on the other hand, is fixed by electrostatic attraction to the iodide ion, which does not move so readily.

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Doping process

• The halogen doping transforms polyacetylene to a good conductor.

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

Conductivity of typical materials

14http://nobelprize.org/nobel_prizes/chemistry/laureates/2000/public.html

Conductivity of conductive polymers compared to those of other materials, from quartz(insulator) to copper (conductor). Polymers may also have conductivities corresponding to those ofsemiconductors.

Conductivities

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Applications of conductive Polymers

Conducting Polymers have many uses.  The most documented are as follows:

anti-static substances for photographic film

Corrosion Inhibitors

Compact Capacitors

Anti Static Coating

Electromagnetic shielding for computers

"Smart Windows"

Transistors

Light Emitting Diodes (LEDs)

Lasers used in flat televisions

Solar cells

Displays in mobile telephones and mini-format television screensPolymer Science: Emissive Materials Nanomaterials (199), Springer-Verlag Berlin Heidelberg, Heidelberg (Germany), 199-207 (2006) 16

Applications

Shield for computer screen against electromagnetic "smart" windows radiation

Solar cell

Photographic Film Light-emitting diodes 17

Conclusion• For a polymer to conduct free electrons are needed.

• Conjugated polymers are semiconductor materials while doped polymers are conductors.

• Today conductive plastics are being developed for many uses. 18

references• H. Shirakawa, E.J. Louis, A.G. MacDiarmid, C.K. Chiang and A.J.• Heeger, J Chem Soc Chem Comm (1977) 579• T. Ito, H. Shirakawa and S. Ikeda, J.Polym.Sci.,Polym.Chem. Ed. 12

• (1974) 11–20• C.K. Chiang, C.R. Fischer, Y.W. Park, A.J. Heeger, H. Shirakawa, E.J.

• Louis, S.C. Gau and A.G. MacDiarmid , Phys. Rev. Letters 39 (1977)

• 1098• C.K. Chiang, M.A. Druy, S.C. Gau, A.J. Heeger, E.J. Louis, A.G.

• MacDiarmid*, Y.W. Park and H. Shirakawa, J. Am. Chem. Soc. 100 (1978) 1013• Evaristo Riande and Ricardo Díaz-Calleja, Electrical Properties of

Polymers• http://nobelprize.org/nobel_prizes/chemistry/laureates/2000/index.html

• http://www.organicsemiconductors.com 19

THANK YOUTHANK YOU

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• organic semiconductor can be doped either by removing an electron from valence band or adding an electron to the conduction band to increase its conductivity. Doping organic semiconductor creates more charge carriers which move in an electric field. This movement of charge is responsible for electrical conductivity in organic semiconductor. Doping a polymer is different from that of inorganic semiconductor in which elements with excess and shortage of electrons are introduced. In polymer, both doping process involves an oxidation and reduction process. The first method involves exposing a polymer to an oxidant such as iodine or bromine or a reductant such as alkali metals.2 The second is electrochemical doping in which a polymer-coated electrode is suspended in an electrolyte solution. The polymer is insoluble in the solution that contains separate counter and reference electrodes. By applying an electric potential difference between the electrodes, counter ion from the electrolyte diffuses into the polymer in the form of electron addition (n doping) or removal (p doping). 2One of the problem with organic semiconductor is that p-type material is much more prevalent than n-type because electron rich n-type is unstable in the presence of oxygen. Organic semiconductor can only be useful for devices if both p-type and n-type are both incorporated. The most widely used organic semiconductors are pentacene, thiophene oligomers, and regioregular polythiophene.

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