Conducting Polymers powerpoint presentation
- 3. • Those polymers which conduct electricity are called conducting polymers. • The conduction of polymers may be due to unsaturation or due to the presence of externally added ingredients in them. Classification Conducting Polymers Intrinsic conducting polymers Intrinsic polymer with conjugation Doped conducting polymers Extrinsic conducting polymers Conductivity element Blended conducting polymer
- 4. • These polymers are characterized by intensive of double bonds in their structure i.e., backbone of the polymer. I n t r i n s i c C O N D U C T I N G P O LY M E R S ( I C P s ) Classification Conducting polymers having conjugation Doped Conducting polymers
- 5. ❑Polymers having conjugated double bonds in the backbone possess their conductivity due to π electrons. 1. Conducting polymers having conjugation
- 6. ❑Band Theory in Conducting Polymers: Orbital Overlap and Band Formation: When polymers have conjugated double bonds, the π orbitals overlap along the entire polymer backbone. This continuous overlap creates an extended π-system. Energy Bands: In this system, the overlapping π orbitals form two distinct energy bands: Valence Band: This is the lower energy band, filled with electrons. It corresponds to the bonding molecular orbitals. Conduction Band: This is the higher energy band, which is usually empty. It corresponds to the anti-bonding molecular orbitals. Fermi Energy Gap: The energy gap between the valence band and the conduction band is called the Fermi energy gap (or simply the band gap). For electrical conductivity to occur, electrons must move from the valence band to the conduction band, where they are free to move and conduct electricity.
- 7. ❑In π bonding the overlapping of the orbitals is lateral over the entire backbone resulting in the formation of ✓ lower energy valence bands and ✓ higher energy conducting bands which were separated by a significant fermi energy gap. ❑ The electrical conductivity takes place only after thermal or photolytic activation of the electrons, which give them sufficient energy to jump the gap and reach into conduction band. 1. Conducting polymers having conjugation
- 8. Example: Polyacetylene -CH = CH – CH = CH – CH = CH - = CH – CH = CH – CH = CH – CH = Delocalisation of π electrons
- 10. Hence their conductance can be ❑increased by introducing a positive charge or negative charge on polymer backbone by oxidation or reduction. • This process is similar to semiconductor technology and is called Doping. ❑Doping is of two types: ➢ Creating a positive site on polymer backbone called p-doping ➢ Creating a negative site on polymer backbone called n-doping 2. Doped conducting polymers The conducting polymers having π electrons in the backbone can easily be oxidized or reduced because they possess : ✓ low ionization potential and ✓ high electron affinities High electron affinity
- 11. p-doping • p-doping is done by oxidation of a conducting polymer like polyacetylene with Lewis's acid or Iodine vapor
- 12. p-doping • During oxidation process the removal of π electrons from polymer backbone led to the formation of a delocalized radical called ion called polaron having a hole in between valence band and A polaron is a quasiparticle used in condensed matter physics to describe the interaction between an electron and the lattice of a solid material. Fig: Polaron: an electron in a solid interacts with the crystal lattice. As a result, it is 'dressed' by the resulting polarization cloud of nuclear displacements and forms the so-called polaron.
- 13. p-doping • The second oxidation of the polaron results in the two positive charge carriers in each chain called bipolaraon, which are mobile due to delocalization. • These delocalized charge carriers are responsible for conductance when placed in electric field. A bipolaron is a quasiparticle that forms when two polarons, typically two electrons or two holes, become bound together in a solid material.
- 14. p-doping The bipolaron is represented by the paired energy levels, where both levels are occupied within the band gap. In p-doped polyacetylene, doping introduces holes (positive charges) into the polymer chain, which can lead to the formation of solitons.
- 15. p-doping
- 16. n-doping • This is done by reduction process • For this conductance, polymer having conjugation is treated with Lewis's base like sodium naphthalide
- 17. n-doping
- 18. • These polymers possess their conductivity due to the presence of externally added ingredients in them. • These are of two types: E x t r i n s i c a l l y C O N D U C T I N G P O LY M E R S ( E C P s ) Classification Conductive element filled polymers Blended conducting polymers 10.1016/j.progpolymsci.2014.07.007
- 19. âť‘The polymer acts as the binder to hold the conducting elements (such as carbon black, metallic fibers, metallic oxides etc.) together in the solid entity. âť‘ Minimum concentration of conductive filler, which should be added so that polymer starts conducting is known as percolation threshold. âť‘Because at this concentration of filler or conducting element, a conducting path is formed in polymeric material. 1. Conductive element filled polymers
- 20. âť‘The polymer acts as the binder to hold the conducting elements (such as graphite, metallic fibers, metallic oxides etc.) together in the solid entity. âť‘ Minimum concentration of conductive filler, which should be added so that polymer starts conducting is known as percolation threshold. âť‘Because at this concentration of filler or conducting element, a conducting path is formed in polymeric material. âť‘Such compounds have been important, for example in hospital operation theatres where it was essential that static charges did not build up, leading to explosion involving anesthetics. 1. Conductive element filled polymers
- 21. âť‘ These polymers can be obtained by blending processes. âť‘ They possesses better physical, chemical, electrical and mechanical properties and can be easily processed. âť‘ E.g: upto 40% of polypyrrole will have little effect on tensile strength and give much higher impact strength. Such compounds are of interest in electromagnetic shielding. 2. Blended conducting polymers
- 22. Applications of CONDUCTING POLYMERS âť‘Engineering applications of conducting polymers: There are several utilities of conducting polymer due to their better physical, chemical, mechanical properties, lightweight and easy to process. Some of them are: To make rechargeable, lightweight batteries In making of analytical sensors for pH O2, NO2, SO2, glucose making of Ion exchangers
- 23. Applications of CONDUCTING POLYMERS Making of solar cells In photovoltaic devices