Conducting Polymers
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The seminar presented by Abhinav S on September 17, 2019, discusses the journey of conducting polymers from laboratory curiosity to commercial applications. It highlights the fundamental properties of polymers, factors affecting conductivity, and mechanisms for achieving conductivity in these materials, particularly focusing on polyacetylene. Conducting polymers are now utilized in various applications such as batteries, transistors, and biosensors, demonstrating the interdisciplinary expertise required for their development and market introduction.
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✗ The conductivity shows a temperature dependence similar to that of
semiconductors
✗ Obeys the Mott Variable Range Hopping (VRH) model:
✗ 𝜎(T) = 𝜎0 exp [ - (T0 / T)1/(n+1) ]
✗ n is dimension number
✗ 𝜎0 is a factor weakly related to temperature
✗ Conductivity closely related to the doping degree and the degree of
ordering of the polymer main chain
✗ The doping degree relates to the charge carrier concentration](https://image.slidesharecdn.com/seminarconductingpolymers-190925152603/85/Conducting-Polymers-29-320.jpg)
Conducting Polymers
- 1. CONDUCTING POLYMERS From a Lab Curiosity to the Market Place A Seminar On September 17, 2019 Presented By Abhinav S Sri Sathya Sai Institute Of Higher Learning II M.Sc Chemistry
- 2. Introduction Polymers (or plastics as they are also called) are known to have good insulating properties. Polymers are one of the most used materials in the modern world.
- 3. 3 Polymers shape our lives because Polymers can be shaped…
- 4. What is Conductivity ??? ✗ Gas discharges, vacuum tubes, semiconductors known as 1D conductors deviate from ohm’s law. ✗ Conductivity depends on Number of charge carriers and their mobility. ✗ In metals all 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. ✗ Insulators however have tightly bound electrons so that nearly no electron flow occurs so they offer high resistance to charge flow. 4 V = IR
- 5. So for conductance free electrons are needed. 5
- 6. 6 What makes a material conductive?? (Advanced Information) The Nobel Prize in Chemistry, 2000: Conductive polymers
- 7. 7 ✗ Diamond and graphite are modifications of pure carbon, while in polyacetylene one hydrogen atom is bound to each carbon atom. ✗ Diamond – σ bonds (insulator) & high symmetry gives isotropic properties ✗ Graphite and acetylene both have mobile π electrons upon doping gives highly anisotropic metallic conductors. ✗ The conductivity of stretch oriented polyacetylene is some 100 times higher in the stretch direction than perpendicular to it.
- 8. How can plastic become conductive ?? ✗ Plastics are polymers, molecules that form long chains, repeating themselves. ✗ In becoming electrically conductive, a 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 8
- 9. Factors affecting conductivity ✗ Density of charge carriers. ✗ Their mobility. ✗ Direction ✗ Presence of doping materials ✗ Temperature. 9 (Advanced Information) The Nobel Prize in Chemistry, 2000: Conductive polymers
- 10. “Conductive Polymers” A surprise discovery ✗ Polymers – Plastic – opposite to metals ✗ Electric wires coated with polymers for protection ✗ Yet Polyacetylene was made conductive (a breakthrough!!!) 10 Shirokawa Hideki, Nobel Lecture Dec 8, 2000
- 11. 11 Alan J Heeger Hideki Shirakawa Alan G MacDairmid Photos from Nobel Foundation Archive
- 12. 12 POLYACETYLENE Hall, Nina Focus Article 2003 Chem. Commun pp1-4
- 13. 13 When silvery films of the semiconducting polymer, trans‘polyacetylene’, (CH)x, are exposed to chlorine, bromine, or iodine vapour, uptake of halogen occurs, and the conductivity increases markedly (over seven orders of magnitude in the case of iodine) to give, depending on the extent of halogenation, silvery or silvery-black films, some of which have a remarkably high conductivity at room temperature.
- 15. 15 ✗ SOLITON ✗ The soliton ( S) is an unpaired π-electron resembling the charge on free radicals, which can be delocalized on a long conjugated polymer main chain. ✗ Neutral soliton oxidise to give +ve soliton and reduce to give –ve soliton ✗ The soliton possesses a spin of ½ and no spin for +ve or –ve soliton ✗ Electronic energy level of the soliton is located at the middle of the bandgap of the trans polyacetylene.
- 16. 16 ✗ POLARONS ✗ Major charge-carriers in conducting polymers including basic state degenerate trans-polyacetylene and the basic state non- degenerate conjugated polymers. ✗ Positive (P+) and negative (P-) polarons formed after oxidation and reduction of the conjugated polymer main chain respectively. ✗ Possess spin of ½ ✗ The appearance of the polarons produces two new polaron energy levels in the bandgap of the conjugated polymers.
- 17. 17 ✗ BIPOLARONS ✗ Charge carrier that possesses double charges by coupling of two P+ or two P− on a conjugated polymer main chain ✗ Can be formed when the concentration of polarons are high in the conjugated polymer main chains. ✗ No spin ✗ Positive bipolaron and negative bipolaron correspond to the hole pair or the electron pair.
- 18. 18 Conduction band Valance band Neutral soliton S0 Negatively charged Soliton S- Positively charged Soliton S+
- 19. 19 Isolated solitons are not stable in polymers, charge exchange will lead to the formation of S0-S+ (or S0-S-) pairs, which will be strongly localized to form a polaron
- 20. 20 ✗ Two Polarons may collapse to form a bipolaron having zero spin with charges. ✗ Two Charges are not independent but move as pair.
- 21. 21 Undisturbed Conjugation Free Radical Carbocation Carbanion Neutral Soliton Positive Soliton Negative Soliton
- 22. 22 Positive Polaron Negative Polaron Negative Bipolaron Positive Bipolaron Radical anion Radical cation Carbodication Carbodianion
- 24. 24 ✗ Chemical Doping ✗ Includes p type doping and n type doping ✗ p doping (oxidative doping) refers to oxidation of conjugated polymers to form polarons ✗ After doping conjugate polymer loses electron and oxidises - dopant gains electron – become counteranion ✗ CP + (3/2) I2 CP+(I3) – ✗ Examples – oxidants I2 Br2 AsF5 etc.
- 25. 25 ✗ N doping(reduction doping) refers to the reduction process of the conjugated polymer main chain to form negative charge carriers. ✗ After doping the conjugated polymer is reduced and gains electrons & e dopant losses an electron to become the countercation. ✗ CP + Na+(C10H8)- CP-(Na)+ + C10H8 ✗ Examples - strong reductants, such as alkali metal vapor, Na+(C10H8)-
- 26. 26 ✗ Electrochemical Doping ✗ Involves electrochemical oxidation or reduction of conjugated polymer on an electrode ✗ For electrochemical p-doping - conjugated polymer oxidized & doping of counteranions from electrolyte solution occur: ✗ CP – e- + A- CP+ + A- ✗ For electrochemical n-doping - conjugated polymer reduces & doping of countercations from electrolyte solution occur: ✗ CP + e- + M+ CP- + M+
- 28. 28 ✗ Conductivity is the most important property of conducting polymers. ✗ Normally 10-9 to 10-6 S/cm but after doping six to nine folds. ✗ The highest conductivity reported in the literature is 105 S/cm for drawing-extended ordering conducting polyacetylene film. ✗ Have an amorphous structure. ✗ Charge carriers are located in the local doping energy levels and charge carriers move easily but charges hop for transportation. ✗ Activation energy for hoping is higher.
- 29. 29 ✗ The conductivity shows a temperature dependence similar to that of semiconductors ✗ Obeys the Mott Variable Range Hopping (VRH) model: ✗ 𝜎(T) = 𝜎0 exp [ - (T0 / T)1/(n+1) ] ✗ n is dimension number ✗ 𝜎0 is a factor weakly related to temperature ✗ Conductivity closely related to the doping degree and the degree of ordering of the polymer main chain ✗ The doping degree relates to the charge carrier concentration
- 30. 30 Dependence of the conductivity of polyacetylene on the conjugation length. Doping level: 3.5% (iodine), data taken at room temperature. Siegmar Roth and Maria Filzmoser,Conducting Polymers – thirteen years of polyacetylene doping, Advanced Materials, 1990
- 32. Applications 32
- 33. Conducting polymers have many uses. The most documented are as follows: ✗ Corrosion Inhibitors ✗ Compact capacitors ✗ Anti Static Coating ✗ Electromagnetic sheilding for computers ✗ Anti static substances for photographic films. ✗ Batteries ✗ Transistors ✗ Light Emitting Diodes (LEDs) ✗ Lasers used in flat televisions ✗ Solar cells ✗ Mobile phone displays ✗ Biosensors
- 34. “Conducting polymers have, thus, come a long way from purely laboratory curiosity to a class of materials that can find end use in a wide variety of commercial products, ranging from batteries to biosensors. Such a development is a classic example that serves to illustrate the wide range of expertise, starting from chemists, physicists, biologists and technologists, that is required to take some invention in the laboratory to the market place.” 34 https://www.polymersolutions.com/blog/demand-grows-for-conductive-polymers/
- 35. Credits ✗ Presentation template by SlidesCarnival This presentation uses the following typographies: ✗ Titles: Inconsolata & Brush Script MT ✗ Body copy: Pangolin & Arial https://www.fontsquirrel.com/fonts/inconsolata https://www.urbanfonts.com/fonts/Pangolin.font 35
- 36. REFERENCES ✗ H. Shirakawa, E.J. Louis, A.G. MacDiarmid, C.K. Chiang and A.J.Heeger, J Chem Soc Chem Comm (1977) 579 ✗ http://nobelprize.org/nobel_prizes/chemistry/laureates/2000/index.html ✗ (Advanced Information) The Nobel Prize in Chemistry, 2000: Conductive polymers Kungl. Vetenskapsademien, The Royal Swedish Academy Of Sciences ✗ Yongfang Li , Organic Optoelectronic Materials, Springer International Publications, 2015, pg 23 – 50 ✗ Ramakrishnan S, Conducting Polymers: From Lab curiosity to the Market Place, Resonance, vol 2, No.11 pp 48 - 58 ✗ Siegmar Roth and Maria Filzmoser,Conducting Polymers – thirteen years of polyacetylene doping, Advanced Materials, 1990 36