1. PHYSICAL CHEMISTRY PRESENTATION (SPECIAL-III) TOPIC: CONDUCTING POLYMERS

2. Content 1.Introduction 2.Classification of conducting polymers 3.Intrinsically conducting polymers (ICPs) 4.Extrinsically conducting polymers (ECPs) 5.Synthesis of conducting polymers 6.Factors influencing the conductivity of polymers 7.References

3. INTRODUCTION Introduction  Conducting polymers are organic materials that have the unique property of being able to conduct electricity.  This is due to the presence of conjugated pi electrons in their polymer chains, which allow the efficient transfer of electrons between adjacent molecules.  One of the most promising applications of conducting polymers is in biomedicine.  They can also be used in the development of neural interfaces, such as those used in brain-computer interfaces.

4. Classification of Conducting Polymers  Conducting polymers are classified according to their composition into two categories:

5. Intrinsically Conducting Polymers (ICPs)  Intrinsically conducting polymers are substances which have a π-bond backbone.  These π-electrons flow from one point to another in the polymer which results to their ability to conduct electricity.  The conjugation can be due to either π electrons or due to doped ingredients.  On the basis of above point they can be further classified into: 1.Conjugated Conducting Polymers 2.Doped Conducting Polymers

6. Conjugated Conducting Polymers  In these types of polymers, due to the presence of double bonds and lone pair of electrons conduction of electricity takes place.  Due to overlapping of conjugated π electrons, valence and conduction bands throughout the backbone of the polymer results into conduction of electricity.  Electrical conduction can occur only after attainment of required energy of activation either thermally or photochemically because there is some gap between the valence and conduction bands. So the electrons need to be excited by some means.  Ex: Polyacetylene, polyaniline, etc.

7. Doped Conducting Polymers  These polymers are made by adding some foreign material or desired impurities which enhance their conduction power.  These impurities are called doping agent or dopant.  The increase in conduction is due to participation of impurity elements in between the valence band and conduction band.  They make a bridge through which electrons can jump easily from the valence band to the conduction band.  Doping is process of developing positive or negative charge through oxidation or reduction of the semiconductor.  Doping are mainly two types:

8. 1)p-type doping through oxidation of materials: In this type of doping some electrons from the conjugated π bonds are removed through oxidation creating a positive hole called polaron inside the polymer. The positive hole or polaron can move throughout the polymeric chain and make it conducting polymer. 2)n-type doping through reduction of materials: In this type of doping some electrons are introduced to the conjugated π bonds through reduction creating a negative hole or charge inside the polymer. The negative hole or charge can move throughout the polymeric chain and make it conducting polymer.

9. Extrinsically Conducting Polymers (ECPs)  Those conducting polymers which have their conductivity due to the presence of externally added ingredients in them are called extrinsically conducting polymers.  On addition of carbon black or some metal oxides or metallic fibers, the polymer becomes conductive.  The minimum concentration of the element required for conductivity is called percolation threshold.  ECPs are of two types: 1.Conducting Elements Filled Polymers (CEFP) 2.Blended conducting polymers (BCP)

10. Conducting Elements Filled Polymers  In this type of ECPs a conducting element is added to the polymer.  The polymer acts as a binder to hold the conducting elements together in solid entity.  When carbon black or some metal oxides or metal fibres are added to the polymer it becomes conductive.  They possess good bulk conductivity.  They are cheaper.  They are light in weight.  They are mechanically durable and strong.  They are easily processable in different forms, shapes and sizes.

11. Blended conducting polymers  These types of polymers are obtained by blending a conventional polymer with a conducting polymer either physically or chemically.  This blend of polymers conduct electricity.  These polymers can be easily processed.  They possess better physical, chemical and mechanical properties.

12. Synthesis of conducting polymers  Synthesis of conducting polymers can be done in following ways: 1.Chemical method 2.Electrochemical method 3.Dehydrogenation

13. Chemical method  Conducting polymers have been chemically synthesized through oxidation or reduction of monomers and polymerization of corresponding monomers.  One of its advantages is the chance of mass production at a reasonable price.  For example, poly (3-hexylthiophene) is renowned and frequently studied conducting polymer which is generally produced by chemical method.  Polypyrrole and Polyaniline can be prepared chemically.  For chemical polymerization the basic need after conjugation is stability.

16. Electrochemical Method  Electrochemical synthesis of conducting polymers is very important among the different methods of synthesis, since it is simple, cost-effective, can be performed in a single section glass cell, reproducible and the fabricated films have required thickness and uniformity.  The most widespread electrochemical technique for preparation of conducting polymers is anodic oxidation of appropriate electroactive functional monomer, cathodic reduction is used much less often.  A simplified means of electro polymerization of an electro active monomer, such as pyrrole or thiophene engaged alternate chemical and electrode reaction steps.  The electro (co)polymerization means inserting three electrodes (reference electrode, counter electrode and working electrode) into solution including reactors or monomers. By applying voltage to electrodes, redox reaction to synthesize polymer is promoted.

18. Dehydrogenation

19.  Synthesis of Acetylene:  Different forms of Polyacetylene: Synthesis of different polymer

20.  Synthesis of doped polyacetylene conducting polymers:  Synthesis of Poly(p-phenylene Sulphide) PPS: (1) (2)

21. Factors influencing the conductivity of polymers  The conductivity of organic polymers is influenced by the following factors: 1.Chain length: The conductivity of a polymer increases with the increase in the length of the polymer chain and increase in the number of conjugation. 2.Doping level: The conductivity of a polymer increases with the increase in doping level till the saturation point is reached. 3.Frequency of current: Conductivity of a polymer depends on the frequency of current as doping is the transport mechanism in these materials. 4.Charge Carriers: When charge carriers (from the addition or removal of electrons) are introduced into the conduction or valence bands (see below) the electrical conductivity increases dramatically. Technically almost all known conductive polymers are semiconductors due to the band structure and low electronic mobility. 5.Conjugation: Conjugation means that the polymer backbone consists of alternating single and double bonds. The strong chemical bonds between the carbon atoms are the so-called localized σ bonds, whereas the double bonds provide weaker and less strongly localized π bonds. However, the conductivity of these polymers is rather low.

22. 6.Effect of Temperature: Conductivity of a polymer increases with increase in temperature. Sometimes, the conductivity becomes constant at a particular temperature. The polymer formed at high temperature has higher conductivity and is stronger than that formed at lower temperature. Ex. Silver conductivity increase with falling temperature and polyacetylene conductivity increases with increasing temperature.

23. References Pratt C (2015) Applications of conducting polymers. http://homepage.ntlworld.com/colin.pratt/applcp.pdf Application of Conducting Polymers in Solar Water-Splitting Catalysis by Mohammed Alsultan, Abbas Ranjbar, Gerhard F. Swiegers, Gordon G. Wallace, Sivakumar Balakrishnan, and Junhua Huang, School of Chemistry, Monash University, Clayton, VIC 3800, Australia. Conducting Polymers, Fundamentals and Applications. https://link.springer.com/book/10.1007/978-1- 4615-5245-1 Handbook of Conducting Polymers, Second Edition, Revised and Expanded. https://www.researchgate.net/publication/233812251_Handbook_of_Conducting_Polymers_Second_Edit ion_Revised_and_Expanded Synthesis and Characterization of a Conductive Polymer Blend Based on PEDOT: PSS and Its Electromagnetic Applications. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8840719/

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