Study on Conducting

Polymer :Polyaniline

DHEERAJ KUMAR

M.Sc (Polymer Science & Technology)

Department of Applied Chemistry

OUTLINE

Introduction

What is Polymer ?

Types of Polymer ?

Conducting polymer

Types of Conducting Polymers.

Types of Conduction

Doping

Polyaniline

Synthesis

Properties

Polyaniline nanowires

Synthesis of Polyaniline Nanowires

Applications

Conclusions

POLYMER

The word ‘polymer’ comes from the Greek words

poly (meaning ‘many’) and meros (meaning ‘parts’).

Example: POLYBUTADIENE =

(BUTADIENE+ BUTADIENE+......)n

Where n = 4,000

Polymers are very large molecules made when hundreds of monomers

join together to form long chains.

Importance of Polymers Common used in TV, Radio, Computer,Bags, Automobile

Tyres,Flooring Materials, Electrical Components etc…

Properties- Light weight, High strength, Flexible,Chemical

resistant.

Types of Polymers

A Polymer whose backbone chain is essentially made of

carbon atoms is termed an ‘Organic polymer’.

Examples- cellulose, proteins, polyethylene, nylons.

A Polymer which does not have carbon atom in their

chain is termed as ‘Inorganic polymer’ .

Examples- Glass and silicone rubber

Molecular Structure of Polymer

Linear

High Density Polyethylene (HDPE), PVC, Nylon,

Cotton(Well packed structure).

Branched

Low Density

Lower tensile strength

Lower melting point

- Polyethylene (LDPE)

Cross-linked or Networks

Hard, Rigid,Brittle

Bakelight,Formaldehyde Resin

Melamine,Kevlar, Epoxy

POLYMERISATION The process by which the monomer molecules are linked

to form a big polymer molecule is called ‘Polymerisation’.

Polymerisation is a process of bonding monomer, or

“single units” together through a variety of reaction

mechanisms to form longer chains named Polymer.

e.g

nEthene + nEthene = (Polyethene)n

Addition Polymerization(A.P)=

When monomers just add on to form the polymer,

Without the elimination of any product ,the process is

called ‘Addition polymerisation’.

e.g. Ethylene monomers add on to form

polyethylene. (5 Ethylene monomers)

Polyethylene formation

CONT….

Condensation Polymerisation(C.P)= Monomers react together with the elimination of small molecules like

H2O,NH3 or ROH, etc…

In A. P. mol. weight of polymer is roughly equal to that of all

monomers, while in C. P. the mol. weight of polymer is lesser by the

weight of simple molecules eliminated during the condensation

process. E.g. Condensation polymerisation diacid

diamine.

Conducting PolymersConducting polymers are those polymers

which

Conduct electricity due to delocalization of

π electrons.

E.g- Polyacetylene, Polythiophene,

Polyaniline ,Polypyrrole etc.

Types of Conducting Poymers

The main

chain contains

Heteroatoms present

No heteroatomNitrogen-

containingSulfur-containing

Aromatic

cycles

•Poly(fluorene)s

•polyphenylenes

•polypyrenes

•polyazulenes

•polynaphthalenes

•The N is in the

aromatic

cycle:poly(pyrrole

)s (PPY)

•polycarbazoles

•polyindoles

•polyazepines

The N is outside

the aromatic cycle:

•polyanilines (PA

NI)

•The S is in the

aromatic

cycle:poly(thiophe

ne)s (PT)

•poly(3,4-

ethylenedioxythio

phene) (PEDOT)

The S is outside

the aromatic cycle:

•poly(p-phenylene

sulfide) (PPS)

Double

bonds

•Poly(acetylene)s

(PAC)

Aromatic

cycles and

double bonds

•Poly(p-

phenylene

vinylene) (PPV)

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 , redoxbehavior , catalytic properties, electrochemical effects, Photoactivity, Junction effects

Mechanical - light weight , flexible , non metallic surface properties

What is Conductivity?Conductivity can be defined simply by Ohms Law.

V= IR

Where R is the resistance, I the current and V the voltagepresent in the material.

The conductivity depends on the number of chargecarriers (number of electrons) in the material and theirmobility.

In a metal it is assumed that all the outer electrons are free to carry charge and the impedance to flow of charge is mainly due to the electrons "bumping" in toeach other.

Types of Conduction Intrinsic conductors(Pure)- Conduct electricity in pure

form due to the presence of electrons & holes.

Extrinsic conductors- By adding external

impurities.(Doping)

Holes- Formed by removal of electrons on doping.

Two conditions to become

conductive:

1-The first condition for this is that the polymer consists of

alternating single and double bonds, called conjugated

double bonds.

In conjugation, the bonds between the carbon atoms are

alternatevly single and double. Every bond contains a

localised “sigma” (σ) bond which forms a strong

chemical bond. In addition, every double bond also

contains a less strongly localised “pi” (π) bond which is

weaker.

(2) DopingConverstion of poymer back bone to a charge π

conjugated system is called Doping.

There are diffrents types of Doping-

*Redox doping

*Non redox doping

*Photo doping

*Charge injection doping

*Electrochemical Doping

TYPES OF DOPING AGENTS

Dopants may be classified as:

Neutral dopants: I2, Br2, AsF2, Na, K,

H2SO4, FeCl3 etc.

Ionic dopants: LiClO4, FeClO4, CF3SO3Na,

BuNClO4 etc.

Organic dopants: CF3COOH, CF3SO3Na, p-

CH3C6H4SO3H

Polymeric dopants: PVS, PPS

Plot of conductivity vs doping

Conductivity increases upto a certain doping level

200

100

0.0 0.1 0.2Doping level (dopant/CH unit)

Conductivity

(S/cm)

Effect of dopant

•Conductivity - increases upto a

certain doping level .

•Stability – decreases

•Morphology : due to presence of

charges shape will not be retained.

Polyaniline

Polyaniline (PANI) is a conducting polymer of

the semi-flexible rod polymer family.

Produced as bulk powder, cast films, or fibers.

One of the oldest known conducting polymer.

First discovered in the 19th century.

Also known as Aniline Black.

Synthesis of Polyaniline

Found in one of three idealized oxidation states.

leucoemeraldine – white/clear & colorless (C6H4NH)n

emeraldine – green for the emeraldine salt, blue for the emeraldine base ([C6H4NH]2[C6H4N]2)n

(per)nigraniline – blue/violet (C6H4N)n

The formation of leucoemeraldine can be described as follows, where [O] is a generic oxidant.

n C6H5NH2 + [O] → [C6H4NH]n + H2O

The most common oxidant is Ammonium persulfate.

The reaction is very exothermic

Structure

Polyaniline Nanowires

One dimensional polyaniline nanowire is an electrically conducting

polymer that can be used as an active layer for sensors whose

conductivity change can be used to detect chemical or biological

species.

Polyaniline naowires

Why Polyaniline?

• High sensitive

• Very simple in detection

• Rapid

• Flexibile

• Easy in synthesis

Synthesis of Polyaniline

Nanowires

1) Chemical Synthesis-Polyaniline

nanowires are formed by chemical

oxidation of aniline monomers.

2)Electrochemical polymerization-Aniline monomers are electrochemically

oxidized and polymerized on the surface of

the anode of the electrochemical cell.

Electrochemical Polymerization Polyaniline can be synthesized by anodic oxidation of

aniline monomers through an inert electrode .

One of the key advantages of the electrochemical

method is that this technique allows direct deposition

of polyaniline nanostructures onto metal electrodes in

a simple and cost effective .

Electropolymerization of polyaniline can be

categorized into three types: potentiostatic,

galvanostatic, and potentiodynamic growth.

Applications

Conducting polymers have many uses. The mostdocumented 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 beendeveloped these have industrial uses like:

Transistors

Light Emitting Diodes (LEDs)

Lasers used in flat televisions

Solar cells

Displays in mobile telephones and mini-formattelevision screens

Photographic Film

smart" windows

Shield for computer screen

against electromagnetic

"smart" windows

radiation

Light-emitting diodes Solar cell

Conclusion

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.