Conducting-Polymers

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Introduction

Conducting Polymers:

After the first report of a conducting polymer (polyacetylene) in 1977 by Shirakawa, Heeger and Mac Diarmid [1], conducting polymers have attracted the interest of researchers as they show interesting electrical, electronic, magnetic and optical properties. The possibility of combining in these new materials the properties of organic polymers and the electronic properties of semiconductors has been the driving force for various applications [2-4]. Main applications for conducting polymers are based on their electroactivity and conductivity properties. By coating an insulator with a very thin layer of conducting polymer it is possible to prevent the build-up of static electricity. Electromagnetic radiation generated from electrical devices can be absorbed by coating the inside of the plastic casing with a conductive surface [5].  

       There are some other applications including anti-corrosion coatings, sensors, batteries and supercapacitors, and more recently light emitting diodes (LEDs) [6], electrochromic devices [7] and transparent electrode materials. Among different conducting polymers, great attention has been recently devoted to poly (3,4-ethylenedioxythiophene) (PEDOT), which shows quite high conductivity, stability and optical transparency in its conducting state[8]. 

Synthesis of Conducting Polymers

Conducting polymers can be synthesised chemically or electrochemically. Electrochemical polymerisation is very popular since it is a clean method 

and the thickness of polymer and the morphology can be controlled. Films of electronically conducting polymers are generally deposited onto a 

supporting electrode surface by anodic oxidation (electropolymerization) of the corresponding monomer in the presence of an electrolyte solution.

 Different electrochemical techniques can be used including potentiostatic (constant-potential), galvanostatic (constant current) and potentiodynamic

 (potential scanning e.g. cyclic voltammetry) methods [13].

C.M. Li and his colleagues deposited polypyrrole thin films by cyclovoltammetric (CV), galvanostatic and potentiostatic deposition methods.

 The results showed that galvanostatic deposition of polypyrrole film could produce highest electrochemical reactivity in comparison to cyclic

 voltammetry and potentiostatic deposition methods [14].

Chemical Polymerisation

       In the chemical method, a monomer such as pyrrole is often polymerized in an aqueous solution with an oxidant such as ferric sulphate, 

ferric chloride, ammonium persulphate or hydrogen peroxide. The chemical method is suitable for commercial mass production because it is easier

 to control the molecular weight and structure. Polypyrrole formed by chemical polymerisation is often in powder form [15].

electrochemical polymerisation

        In the electrochemical polymerization method, the monomer, dissolved in an appropriate solvent containing the desired anionic doping salt, 

is oxidized at the surface of working electrode by application of an anodic potential (oxidation). As a result of the initial oxidation, the radical cation 

of the monomer is formed and reacts with other monomers present in solution to form oligomeric products and then the polymer. The extended 

conjugation in the polymer results in lowering of the oxidation potential compared to the monomer. Therefore, the synthesis and doping of the 

polymer are generally done simultaneously. The anion is incorporated into the polymer to ensure the electrical neutrality of the film and, at the end of

 the reaction, a polymeric film of controllable thickness is formed at the anode. The anode can be made of a variety of materials including platinum, 

gold, glassy carbon, and tin or indium–tin oxide (ITO) coated glass [16,17].

       The electropolymerization is generally achieved by potentiostatic (constant potential) or galvanostatic (constant current) methods. A typical 

setup (three-electrode cell) for these measurements is schematically shown in Fig. 1.6.