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CONDUCTING POLYMERS

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  • Dear Ms. Agarwal,Solar cell,battery or displays though contain arond 90% of this market,but there are other uses too,eg. polypyrrole can be used as a radar absorbent aterial for fighter aircrafts also.
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CONDUCTING POLYMERS

  1. 1. CONDUCTING POLYMERS Presented by: Rakhi Agarwal
  2. 2. Introduction to Polymers
  3. 3. Polymer basics • Long chain like molecular structure where repeated molecular units are connected by covalent bonds • Polymers used as insulators eg. polyethylene • Variation in crystallization and orientation results in vast morphologies of polymers today • Properties of polymers: - good chemical resistivity at room temperature - low density and Young’s modulus - brittleness at low temperatures - can be stretched to form films
  4. 4. Organic polymers - few examples Polyvinyl Chloride (PVC) (-C2H3Cl-)n Vinyl chloride n(C2H3Cl) Polyethylene (-C2H4-)n Ethylene n(C2H4) Polymer obtainedMonomer unit
  5. 5. Classification based on temperature • Two types - thermoplastic and thermosetting • Thermoplastic - soft and deformable upon heating , heating process is reversible , eg : linear polymers like PVC • Thermosetting - becomes hard and rigid upon heating , heating process is irreversible , eg : network polymers like phenol formaldehyde
  6. 6. Discovery of conducting polymers • Discovered in the late seventies (1977) by Alan Heegar , Dr. Hideki Shirakawa and Alan Macdiarmid. • Before that polymers were used as insulators in the electronic industry. • Advantages over conductors: Chemical - ion transport possible , redox behavior , catalytic properties, electrochemical effects, Photoactivity, Junction effects. Mechanical - light weight , flexible , non metallic surface properties.
  7. 7. Classification of conducting polymers
  8. 8. Electron-conducting polymers Polyacetylene • First conducting polymer to be synthesized • Best defined system • Reaction conditions allow to control the morphology of the polymer to be obtained as gel, powder, spongy mass or a film • Doped with iodine • Inherent insolubility and infusibility impose barriers to the processing of the polymer
  9. 9. • Synthesized by Dehydrohalogenations of vinyl chlorides: Polymers prepared by this route have short conjugation length, structural defects and crosslinks
  10. 10. Precursor routes: Durham route Polymers prepared by this route are continuous solid films, have controlled morphology range and can be stretched prior to conversion
  11. 11. Conduction mechanism • R and L forms are interconverted through a charge carrier soliton • Soliton is a mobile, charged or a neutral defect or a kink in the polymer chain • It propagates down the polymer chain • For short chains Kivelson mechanism is involved
  12. 12. Contrast between isomers of polyacetylene 170`C10^-7trans -77`C10^-13cis structureObtainable temperature Conductivity (siemens/cm) isomer
  13. 13. Doping in polyacetylene • Amount of dopant used is significantly higher • Doped polyacetylene is always in tans form • Neutral polyacetylene can be doped in two ways p type doping : oxidation with anions eg : ClO4(-) n type doping : reduction with cations eg : Na(+) - e + ClO4(-) + ClO4(-) + e + Na(+) (-) Na(+)
  14. 14. Method of doping •Chemical oxidants : iodine , nitronium species , transition metal salts •Chemical reducing agents : sodium naphthamide •Electrochemical methods : used dopants ClO4(-) , BF4(-) and other complex species
  15. 15. Doping with Iodine
  16. 16. Effect of dopant •Conductivity - increases upto a certain doping level •Stability - decreases •Morphology : due to presence of charges shape will not be retained - reason why doped polyacetylene is always trans
  17. 17. Plot of conductivity vs doping Conductivity increases upto a certain doping level 200 100 0.0 0.1 0.2 Doping level (dopant/CH unit) Conductivity (S/cm)
  18. 18. Polypyrrole •Hetero atomic polymers •More stable •Easy to prepare •Greater opportunity to functionalize
  19. 19. Disadvantages of polypyrrole •High cost •Difficult in processing •Lack of mechanical stability after doping •Difficult to fabricate
  20. 20. Various Applications
  21. 21. Coatings • Prevents buildup of static charge in insulators • Absorbs the harmful radiation from electrical appliances which are harmful to the nearby appliances • Polymerization of conducting plastics used in circuit boards
  22. 22. Sensors(to gases and solns.) • Polypyrroles can detect NO2 and NH3 gases by changing its conductivity • Biosensor : polymerization of polyacetylene in presence of enzyme glucose oxidase and suitable redox mediator like triiodide will give rise to a polymer which acts as glucose sensor
  23. 23. Biocompatible Polymers • Artificial nerves • Brain cells
  24. 24. Batteries • Light weight • Rechargeable • Example - Polypyrrole - Li & Polyaniline - Li
  25. 25. Displays • Flat panels • Related problems : low life time & long switching time
  26. 26. Conductive Adhesive • Monomers are placed between two conducting plates and it allows it to polymerize • Conducting objects can be stuck together yet allowing electric current to pass through the bonds

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