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Conducting Polymers

3RD DIGITAL ASSIGNMENT

ENGINEERING CHEMISTRY

E2 SLOT B.TECH-IT

Polymers are usually organic substances composed of a very large

number of like molecules.

Polymers are divided, on the basis of their mechanical properties and

strength, into three categories: rubbers or elastomers, plastics and

fibers.

Polymers are generally insulators because the organic molecules of

which they are composed have no free electrons to carry current; all

the electrons are held firmly by atoms forming the molecules.

Polymers in which the carbon atoms in the backbone are linked by

double bonds have the potential to conduct electricity, especially

when a number of such bonds occur in the vicinity of each other are

known as Conducting Polymers.

Conductive polymers or more precisely intrinsically conducting

polymers (ICPs) are organic polymers that conduct electricity.

Such compounds may have metallic conductivity or behave as

semiconductors. Conductive polymers combine the mechanical

properties (flexibility, toughness, malleability, elasticity, etc.) of

plastics with high electrical conductivity. These properties can be

fine-tuned using different methods of organic synthesis.

In 1977, Alan J. Heeger, Alan MacDiarmid and Hideki Shirakawa

proved that polyacetylene doped (oxidised) with iodine has high

conductivity. This research earned them the 2000 Nobel Prize in

Chemistry. It has great applications in day to day life.

INTRODUCTION

MECHANISM OF CONDUCTION

It is generally agreed that the mechanism of conductivity in these polymers is based on the motion of

charged defects within the conjugated framework. The charge carriers, either positive p-type or negative

n-type, are the products of oxidizing or reducing the polymer respectively. The following overview

describes these processes in the context of p-type carriers although the concepts are equally applicable

to n-type carriers.

Conducting polymers have a

continuous chain of sp2

hybridized carbon centers.

It is these π bonds due to

which they conduct.

Two conditions:

Presence of conjugated

double bonds.

Molecule has to be

disturbed- using a

dopant.

Oxidative doping

(halogens): P-type

semiconducting Polymer

Reductive doping (alkali

metals): N-type

semiconducting polymer

HOW DO THEY CONDUCT?

FEW COMMON EXAMPLES OF CONDUCTING POLYMERS

Conducting polymers have many uses. The most documented are as

follows:

Anti-static substances for photographic film

Corrosion Inhibitors

Compact Capacitors

Anti Static Coating

Electromagnetic shielding for computers

"Smart Windows"

A second generation of conducting polymers have been developed

these have industrial uses like:

Transistors

Light Emitting Diodes (LEDs)

Lasers used in flat televisions

Solar cells

Displays in mobile telephones and mini-format television screens

APPLICATIONS OF CONDUCTING POLYMERS

For conductance free

electrons are needed.

Conjugated polymers are

semiconductor materials

while doped polymers are

conductors.

The conductivity of

conductive polymers

decreases with falling

temperature in contrast

to the conductivities of

typical metals, e.g. silver,

which increase with

falling temperature.

Today conductive plastics

are being developed for

many uses.

CONDUCTING POLYMERS

There are two main groups of applications for these polymers. The first group

utilizes their conductivity as its main property. The second group utilizes their

electroactivity.

Group 1 Group 2

Electrostatic materials Molecular electronics

Conducting adhesives Electrical displays

Electromagnetic shielding Chemical biochemical and thermal sensors

Printed circuit boards Rechargeable batteries and solid electrolytes

Artificial nerves Optical computers

Antistatic clothing Ion exchange membranes

Piezoceramics Electromechanical actuators

Diodes/Transistors 'Smart' structures

Aircraft structures Switches

APPLICATIONS OF CONDUCTING POLYMERS

SMART WINDOWS

Shield for computer screen

against electromagnetic

"smart" windows

radiation

Smart Windows

APPLICATIONS

CONCLUSION

Due to their poor processability, conductive polymers have few large-scale applications. They have promise in antistatic materials and they have been incorporated into commercial displays and batteries, but there have had limitations due to the manufacturing costs, material inconsistencies, toxicity, poor solubility in solvents, and inability to directly melt process. Literature suggests they are also promising in organic solar cells, printing electronic circuits, organic light-emitting diodes, actuators, electrochromism, supercapacitors, chemical sensors and biosensors, flexible transparent displays, electromagnetic shielding and possibly replacement for the popular transparent conductor indium tin oxide. Another use is

for microwave-absorbent coatings, particularly radar-absorptive coatings on stealth aircraft. Conducting polymers are rapidly gaining attraction in new applications with increasingly processable materials with better electrical and physical properties and lower costs. The new nanostructured forms of conducting polymers particularly, augment this field with their higher surface area and better dispersability.

With the availability of stable and reproducible dispersions, PEDOT and polyaniline have gained some large scale applications. While PEDOT (poly(3,4-ethylenedioxythiophene)) is mainly used in

antistatic applications and as a transparent conductive layer in form of PEDOT:PSS dispersions (PSS=polystyrene sulfonic acid), polyaniline is widely used for printed circuit board manufacturing – in the final finish, for protecting copper from corrosion and preventing its solderability.