conducting polymers by dheeraj kumar
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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.
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