Transcript of "Microsoft office power point presentation جديد "
Polymers are typically utilized in electrical and electronic
applications as insulators where advantage is taken of their
very high resistivity.
Conducting polymers are unique as possible substitute for
metallic conductor and semiconductor.
Exhibited highly reversible redox behavior and the
unusual combination of properties of metal and plastics.
These have unique condition mechanism and good
environmental stability in present of oxygen and water .
These polymer could be highly promising for many
technological uses because of their chemical versatility,
stability ,prcoessability, don’t break easily, low specific
gravity , longer life time, and low cost .
There are at least four major classes of semiconducting
polymers that have been developed so far. They include
Conjugated conducting polymers.
Charge transfer polymers.
Ionically conducting polymers.
conductively filled polymers.
What is a conducting polymer?
A polymer which can exhibit significant level of
electricity (it is conduct electricity) is termed as
The electricity conductivity is attributed by the present
of free electrons, hole, charged atoms and molecules.
To electron free move there are many condition most be
present; depends up on the type of conducting polymer
( Extrinsic - Intrinsic ).
There are Tree type of conducting polymer :-
Electronic conducting polymer .
Proton conducting polymer .
Ionic conducting polymer .
The electrical properties of direct gap inorganic
semiconductors are determined by their electronic
structures, and the electrons move within discrete energy
states called bands.
The bonding and ant bonding electron , orbitals of the sp2
hybridized , electron materials(e.g. polyenes) generate
energy bands, which are fully occupied band and empty
highest occupied band is called the valence band, and the
lowest unoccupied band is the conduction band. The
energy difference between them is called the band gap.
SEMICONDUCTORS OR INSULATORS
Free electrons needed
for electrical conduction
“applied electric field is
sufficient to generate
large number of free
Due to the band gap,
much more energy
input is necessary to
create charge carriers
conduction band or
holes in valence band”.
The energy difference between them is called the
Electrons must have certain energy to occupy a given
band and need extra energy to move from the valence
band to the conduction band.
The bands should be partially filled in order to be
electrically conducting, as neither empty nor full
bands can carry electricity.
most conventional polymers have full valence bands
and empty conduction
bands, which are separated from each other by a wide
energy gap (Figure 2.1(b)).
conjugated polymers have narrower band gaps
(Figure 2.1(c)) and doping can change their band
structures by either taking electrons from the valence
band (p-doping) or adding electrons to the conduction
Polaron :- When an electron is added (removed) to the
bottom of the conduction band (from the top of the
valence band) of a conjugated polymer (Figure 2.2(a)),
the conduction (valence) band ends up being partially
filled and a radical anion (cation) (Figure 2.2(b)).
formation of polarons causes the injection of states from
the bottom of the conduction band and top of the
valence band into the band gap.
A polaron carries both spin (1/2) and charge (1e).
Addition (removal) of a second electron on a chain
already having a negative (positive) polaron results
in the formation of a bipolaron (spinless) through
dimerization of two polarons, which can lower the
total energy (Figure 2.2(c))
In conjugated polymers with a degenerate ground
state (i.e. twoequivalent resonance forms),the
bipolarons can furtherlower their energy by
dissociating into two spinless solitons at one-half
of the gapenergy (Figure 2.2(d)).
Solitons do not form in conjugated polymers with non
degenerate ground states.
polarons, bipolarons, and/or solitons increases with
the doping level( At high doping levels, the localized
polarons, bipolarons or solitons near to individual
dopant ions could overlap, leading to new energy
bands between and even overlapping the valence and
conduction bands, through which electrons can flow).
The bulk conductivity of conducting polymers should,
in principle, consist of contributions from intra-chain,
inter-chain and inter-domain electron transportations
Picture of conductivity of some
Sp . gv.ConductivityMaterial
110Carbon black fill PE
Factors that affect in conductivity
1) Denesity of charge carriers.
2) Thier mobility.
3) The direction.
4) presence of doping materials (additives that
facilitate the polymer conductivity)
6) Conjugation length of the polymer chain.
7) Doping Level.
8) Frequency of current.
The conductivity of conductive polymers decreases with
falling temperature in contrast to theconductivities
of typical metals, e.g. silver, which increase with falling
Type of conducting polymer
Dopingconducting These polymers have doping of positive
or negative charge on polymer backbone. Conductivities of
this type can be increased by creating positive or negative
charge on polymer backbone by oxidation or reduction.
polymers are polyconjugated structuers (consists of
alternating single and double bonds,called conjugated
double bonds)which are insoulating in puer state ;but
whene trated by an oxidizing or reducing agent can be
converted into polymer salt with electrical conductivities
comparable to metals.
It is done by oxidation process.
Conducting polymers of previous type is treated
with lewis acid (A) or with iodine vapour or iodine
It is done by reduction process.
Conducting polymer of previous type is treated with lewis
base (B) like sodium naphthalide.
In conjugation, the bonds between the carbon
atoms are alternately 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.
These polymers owe their conductivity due to the
presence of externally added ingredients in them.
Conductive element filled polymer:-In this, the
polymer acts as the binder to hold the conducting
element (such as carbon black, metallic fibers,
metallic oxides,etc.) together in the solid entity.
Generally, special conducting grade C-Black is
used as filler which has very high surface area,
more porosity and more of filamentous properties.
BLENDED CONDUCTING POLYMERS
These polymers are obtained by blending a conventional
polymer with a conducting polymer. Such polymers possess
better physical, chemical, electrical and mechanical
properties and they can be easily processed.
For example :-
upto 40% of polypyrrole will have little efffect on tensile
strength than obtained with a carbon-black filled compound
at only 10% loading.
Advantages of conducting polymer
It is being said that ‘one day conducting polymers
may be used in place of metals in electrical wiring.’
They do not corrode.
Synthesis of conducting polymer
Chemical polymerization(Conjugated monomers react with an
excess amount of an oxidant in a suitable solvent, such as acid. The
polymerization takes place spontaneously and requires constant stirring.
Advantage: mass-production at a reasonable cost.
Electrochemical polymerization (Both counter and reference
electrodes (such as platinum) are placed into the solution
containing diluted monomer and electrolyte (the dopant) in a
solvent. After applying a suitable voltage, the polymer film
immediately starts to form on the working electrolyte.
Solid state polymerization.
Conducting polymers have many uses. The most
documented are as follows:
anti-static substances for photographic film
Anti Static Coating
Electromagnetic shielding for computers "Smart
Windows" A second generation of conducting
polymers have been developed these have industrial
Light Emitting Diodes (LEDs).
Lasers used in flat televisions.
Displays in mobile telephones and mini-format
Shield for computer screen
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
Today conductive plastics are being developed for many