Transcript Slide 1

CONDUCTING POLYMERS
LECTURE - PRESENTATION
CHEMISTRY DEPARTMENT
SARDAR PATEL UNIVERSITY
VALLABHVIDYANAGAR
EVERY LIFE
IS UNIQUE
AND HAS A
PURPOSE
ELECTRICAL BEHAVIOUR
OF POLYMERS
SUPER-CONDUCTOR
CONDUCTOR
SEMI-CONDUCTOR
INSULATOR
RESISTENCE
ORDER
INTRA-MOLECULAR BEHAVIOUR
INTER-MOLECULAR BEHAVIOUR
WIRES-LINEAR CHAIN
ORDER-CLOSE-PACKING
UNSATURATION
CONJUGATION
POLYMERISATION
DOPING
Conducting polymers have backbones of contiguous sp2
hybridized carbon centers. One valence electron on each
center resides in a pz orbital, which is orthogonal to the
other three sigma-bonds. The electrons in these delocalized
orbitals have high mobility, when the material is "doped"
by oxidation, which removes some of these delocalized
electrons. Thus the p-orbitals form a band, and the
electrons within this band become mobile when it is
partially emptied. In principle, these same materials can be
doped by reduction, which adds electrons to an otherwise
unfilled band. In practice, most organic conductors are
doped oxidatively to give p-type materials. The redox
doping of organic conductors is analogous to the doping of
silicon semiconductors
Calculations can be made of
highest occupied molecular
orbital energy, lowest
unoccupied molecular orbital
energy, ionization energy,
electron affinity, and
reorganization energy of a
molecular system.
Designing Polymers
The first step in designing a polymer is to ask what kind of
properties one wants:
What kind of solubility do you want?
What kind of solvents are you working with?
Do you want it solid? Crystalline?
Conductive? Semi-conductive? An insulator? Superconductive?
 What kind of flexibility?
What kind of length? Do you need to control the
length?
Do you need anisotropic properties?
Should it be thermally conductive as well as
electrically?
What about mechanical properties ?
Structures of various conductive organic polymers.
Polyphenylenevinylene, polyacetylene, polythiophene (X =
S) and polypyrrole (X = NH), polyaniline (X = N, NH) and
polyphenylene sulfide (X=S).
POLY-ACETYLENES
The year was 1977. Hideki Shirakawa, Alan
MacDiarmid, and Alan Heeger (winners of the 2000
Nobel Prize in Chemistry) published their discovery
that upon reaction with iodine, polyacetylene exhibited
electrical conductivity many orders of magnitude
higher than the neutral unreacted film. Here, it
seemed, was a polymer chain on which electrons
could move—a molecular conductor. Chemists and
physicists who dreamed of lightweight batteries and a
replacement for copper power lines, and the billiondollar market for these products, got their hopes up;
their goal seemed just over the horizon
Three different types of thermoplastic elastomers,
styrenebutadiene-styrene, styrene-isoprene-styrene, and
styreneethylenebutylene-styrene triblock copolymers have
been blended with polyacetylene utilizing various blending
techniques. In one method, acetylene gas was polymerized
with the Ziegler-Natta catalyst in the presence of either the
thermoplastic elastomer film or a hydrocarbon solution of
the thermoplastic elastomer. The resulting
polyacetylene/thermoplastic elastomer blend has been
characterized. Upon doping with either iodine or ferric
chloride, the ultimate conductivities of the blends were
found to be 60–100 Ω−1 cm−1.
Polyacetylene shows catalytic activity in an aqueous
solution for electroless deposition of amorphous alloys.
The catalytic activity of polyacetylene is comparable to
the activity of some highly catalytic metals, i.e., Cu,
steel, and Pt. Modifications of the Shirakawa technique
led to the formation of a foam-like polyacetylene, which
is highly porous and has a low degree of crystallinity.
This material can be used as a catalytic substrate for
the preparation of amorphous metals in bulk form.
.
Helical polyacetylene was synthesized under an asymmetric
reaction field consisting of chiral nematic (N*) liquid crystals
(LCs). The chiral nematic LC was prepared by adding a
chiroptical binaphthol derivative as a chiral dopant to a
mixture of two nematic LCs. Acetylene polymerizations were
carried out using the catalyst titanium tetra-n-butoxidetriethylaluminum dissolved in the chiral nematic LC solvent.
The polyacetylene film was shown to consist of clockwise or
counterclockwise helical structure of fibrils.. The high electrical
conductivities of ~1500 to 1800 siemens per centimeter after
iodine doping and the chiral helicity of these films may be
exploited in electromagnetic and optical applications.
POLY-p-PHENELYNES
Coated substrates are being tested for
transparency in the visible region and for opacity
to RF and IR radiation. China Lake's approach is
to build upon the successful arylene vinylene
polymer chemistry in conducting polymers and
second-order non-linear optical polymers. The
approximate chemical structure of a new polymer
is shown in the figure.
A particularly interesting area of research involves
shifting the absorption bands of the oxidized
polymer (conducting) outof the visible region by
shifting the absorption of the neutral polymer
(insulating) into the IR. This principle is shown in
the figure
Morphological, structural and chemical characterization
demonstrate unambiguously that coaxial nickel/poly(pphenylene vinylene) (PPV) nano-wires have been
successfully synthesized. Moreover, modification of their
optical and magnetic properties due to the nano-scale and
the core–shell structure has been studied. The nickel-PPV
nano-wires exhibit a slightly blue-shifted photoluminescence
(PL), which is directly related to the tubular morphology of
the PPV shell. The ferromagnetic behaviour has been
shown with the magnetization easy axis along the wire axis.
These arrays of coaxial conducting polymer–metal nanowires embedded in a polymer membrane are interesting for
flexible electronics and photovoltaic devices and their
possible use as multifunctional building blocks for bioapplications.
Poly(p-phenylene) (PPP) was chemically synthesized via
oxidative polymerization using benzene and doped with
FeCl3. The electrical conductivity response of the doped PPP
(dPPP) towards CO, H2 and NH3 is investigated. dPPP shows
no electrical conductivity response towards the first two
gases (CO and H2), but it shows a definite negative response
towards NH3. The electrical conductivity sensitivity of dPPP
increases linearly with increasing NH3 concentration. To
improve the sensitivity of the sensor towards NH3, ZSM-5
zeolite is added into the conductive polymer matrix. The
electrical sensitivity of the sensor increases with increasing
zeolite content up to 30%. The PPP/Zeolite composite with
H+ possesses the highest electrical sensitivity of −0.36 since
H+ has the highest acidity, the highest pore volume and
surface area, which combine to induce a more favorable NH3
adsorption and interaction with the conductive polymer.
POLY-PYRROLES
Poly-pyrrole films are formed by casting a
pyrrole derivative (say, 3-hexadecyl pyrrole) in
an organic solvent on an air-water interface where
the water subphase contains an oxidant (FeCl3).
Free pyrrole as the vapor is added to cause
polymerization.
They are excellent conductors.
The use of electrochemically synthesized polypyrrole
film is investigated as a primer for protective coating
on carbon steel. It provides excellent adherence and
corrosion resistance, and is more environmentfriendly. Polypyrrole was galvanostatically
synthesized on carbon steel, and epoxy paint top coat
was applied on it. The corrosion performance was
evaluated using salt spray test, Tafel plots, and
electrochemical impedance spectroscopy. The
performance was compared to that of a commercial
zinc primer. These tests coherently demonstrate that
the use of polypyrrole film inhibits corrosion better
than a zinc primer in salt and acid environments.
Porous, highly uniform and ordered polypyrrole nanowire
and nanotube arrays were fabricated by chemical oxidation
polymerization with the help of a porous anodic aluminium
oxide (AAO) template. Under 0.2 mol/L pyrrole (H2O) and
0.2 mol/L FeCl3 (H2O) pattern, polypyrrole nanowire
arrays were obtained after 2.0 hour's polymerization
reaction in a two-compartment reaction cell. When the
reaction was stopped after 15 minutes, polypyrrole
nanotube arrays have been formed. The diameter,length
and density of compositive nanowires and nanotubes could
be controlled by parameters of AAO template.
POLY-ANILINES
Properties of Polyaniline



Polyaniline’s electrical properties can be
reversibly controlled by charge-transfer
doping and protonation.
Polyaniline is environmentally stable and
inert (noble) where stainless steel is
corroded.
Polyaniline is applicable to electrical,
electrochemical, and optical applications.
Polyaniline is currently used in cell phones
and calculators, and other LCD technology.
Oxidation States and Acid Base Behavior of
Polyaniline (emaraldine, pernigraniline)
A novel room-temperature route to corrosion protect leadcoated plastic grids with an organic metal, namely,
polyaniline, for producing commercial-grade high specificenergy 12 V/45 Ah lead-acid batteries is reported. The
specific energy of these lead-acid batteries is found to be ca.
45 Wh/kg as against about 30 Wh/kg for conventional leadacid batteries.
The new corrosion protection technology with
polyaniline is based on an immense surface ennobling
and the formation of a passivating metal oxide.
Electrically and optically active polyaniline films
doped with camphorsulfonic acid derivatives
were successfully deposited on non-conductive
substrates via chemical vapor phase
polymerization. The polyaniline films grown by
this method not only showed high
electrochemical activity, but also exhibited
optical activity corresponding to the polymer
chains.
Concentrated solutions of high-molecular weight
polyaniline using amines as gel inhibitors:
Certain amine compounds (gel inhibitors) are used
to form highly concentrated, stable solutions of the
emeraldine base form of polyaniline in numerous
organic solvents from which coatings, films and
fibers are readily prepared without problems
associated with rapid gelation which occurs when
concentrated solutions are attempted without the
use of the gel inhibitors of the present invention.
The corrosion inhibition properties of polished
steel plates (low carbon) coated with a
polyaniline (emeraldine base form) blend with
nylon 66 (termed PANi/Ny) via cast method with
formic acid as the solvent. Polyaniline (PANi)
was prepared chemically from aqueous solution
using aniline (0.2 M) as a monomer and
ammonium persulfate (0.2 M) as an oxidant. The
polymer powder produced was changed into
emeraldine base (EB) form after treatment with
dilute ammonia solution (0.5 M) in order to do
further processing.
Aniline electropolymerization on a DNA-modified
glassy carbon electrode gives rise to a stable
composite DNA-polyaniline film possessing redox
activity over a wide range of pH values. The heights
and potentials of the redox peaks linearly depend
on pH in the pH 3.0–8.0 range. It was established
that the inclusion of DNA into the polyaniline
composition enhances considerably the film
conductivity and capacitance in the weakly acid
and weakly alkaline pH regions; this effect is most
pronounced for the reduced polymer form. The
properties of the prepared DNA-polyaniline film
point to its promise for the use in electrochemical
biosensors.
GENERAL
CHARACTERISTICS
The organic metal can display a unique set of
properties:
It is more noble than copper and slightly less noble
than silver.
t can act as a catalyst.
t can build very thin, though conductive and
reactive, layers, or thin transparent conductive
coatings.
Carbon nano-tubes combined with electroactive polymers
are considered to contribute to further progress in nanoelectronics and to the development of improved electronic
and optoelectronic devices.
A common feature of the ORGANIC METALS is a
huge electronic anisotropy originating from their
anisotropic crystal structures. Ratios between
electrical conductivities in different directions reach
values of up to 1 million! Therefore, they are often
considered as quasi-two-dimensional or quasi-onedimensional conductors.
Another remarkable feature characteristic of many
organic metals is strong electron-electron and
electron-phonon interactions.
Plexcore® polymers and printable inks are the key
ingredients in the formation of high-quality organic
layers. Whether for next-generation, power efficient
displays, low-cost, easily available plastic solar cells
or item-level radio-frequency tags, Plexcore®
polymers and inks deliver the performance to drive
the adoption of these devices
From a technology standpoint, all printed electronic
applications require one or more conductive layers
that can be integrated with organic semiconductors,
dielectrics and other conductive films. Plexcore® OC
is a solution-processable, organic conductive ink that
can serve multiple functions in printed electronic
devices. Plexcore® OC inks are ideal for integration
into various printed electronic devices because they
can be tailored to the particular needs of a device.
Additionally, Plexcore® OC inks are chemically and
thermally stable, making them easy to use in the
production environment.
SEMI-CONDUCTORS
METALLO-ORGANIC
POLYMERS
Metal-containing conducting polymers can be
divided into three types, known as types I, II and III
. These are tethered, coupled and incorporated
respectively. Type I polymers have the metal
group tethered to the conjugated backbone by a
linker moiety such as an alkyl group. In these cases
the polymer acts as a conductive electrolyte and the
metal ions act in similar way to an untethered group.
Type II polymers have the metal directly coupled to
the polymer backbone or coupled to the backbone by a
conjugated linker group, which makes it easier for the
polymer and the metal group to affect each other's
properties directly. Since conducting polymer
backbone and many metal ions are redox-active,
systems can be electrochemically tuned.
The third type of polymer has the metal group
directly incorporated into the conjugated
backbone. In this type the metal group has the
greatest influence on the properties of the
conducting polymer.
The ability to alter the oxidation state of the metal ion,
and thus the charge density along the polymer
backbone, provides an alternative route to charge
carrier creation as opposed to redox doping.
Several methods of synthesizing these polymers are
possible. These include condensation , ring opening
metathesis and electropolymerisation.
Electropolymerisation is a common method
for synthesizing types I and II and often results in
insoluble thin films of polymer being made. The
insolubility of these films can make their
characterization difficult, as solution methods cannot
be used.
Many of these type I and II polymers are based
upon heterocyclic aromatic compounds such as
pyrrole and thiophene.
Most type III polymers cannot be electrochemically
synthesized.
Only thiophene based type III
polymers
have been successfully electropolymerised.
Ring opening and condensation methods are
more commonly used to prepare this type of
polymers. Examples include ferrocene based
polymers,polysilanes and metal polychelates of bischelating ligands.
We were the first to prepare and study
type III metal-ligand semiconductors.
The ligands prepared were 1,5 diformyl
2,6 dihydroxy naphthalene and 1,5
diacetyl 2,6 dihydroxy naphthalene
and their oximes. Cu(II), Ni(II) and
Co(II) chelates of these ligands were
investigated for their conducting
behaviour.
Polyamides and their poly chelates have
values at
298K of about 10– 6 to 10-11 ohm-1 cm-1. Marcu and
Dima3 have prepared the polymers of dimethyl–4,4'–[p–
phenylene–bis (methylidene nitrilo)] disalicylate with
Co(II), Ni(II) and Cu(II) in DMF and reported that these
polymers are heat stable, semi conducting in nature. Semiconducting properties of poly chelates of 2, 5–dihydroxy
phthaldehyde and series of tetra amino compounds have
been reported.
Coordination polymers of Cu(II) and Ni(II) with ethylene
diaminetetrahalato and tetra thioazalatotetrathio flavane
were prepared and their electrical conductivity has been
studied
Electrical conductivity studies on Co(II), Cu(II), Ni(II) and
Cd(II) complexes of azines derived from benzophenone
hydrozone with different aldehydes in presence of few
drops of concentrated hydrochloric acid in alcoholic
medium have been reported..
A number of complexes and other metal
containing groups can be tethered to a conjugated
polymer backbone. These include various
porphyrin complexes, ferrocene, bipyridyl
groups, and crown ether complexes.
ferrocene
porphyrin
crown ethers: 12-crown-4, 15-crown-5, 18-crown-6, dibenzo-18-crown-6, and diaza-18crown-6
SUPERCONDUCTORS
A superconducting polymer is the latest innovation
to emerge from the recent explosion of research into
organic superconductors. Bertram Batlogg and
colleagues at Bell Laboratories in the US have
achieved resistance-free current flow in poly(3hexylthiophene) at 2.35 kelvin.
Batlogg and co-workers allowed a solution of
poly(3-hexylthiophene) - or P3HTP - to solidify
into thin films. The films were found to consist of
tiny crystals of polymer interspersed with
amorphous regions. Resistance-free current flows
when the films are cooled below 2.35 K, and the
relationship between conductivity and temperature
is typical of that in polycrystalline superconductors.
This is thought to result from the co-existence of
the superconducting nanocrystals and the
insulating amorphous areas.
NON-POLYMERIC CONDUCTORS
CHARGE-TRANSFER COMPLEXES
Most materials composed of organic molecules are
normally not metals because of hybridization which
leaves their conduction and valence bands filled. This
property was first overcome by combining planar
organic molecules with non-organic anions (ClO4,
PF6 etc.) which serve as acceptors or donors thus
resulting in the appearance of partially filled
conduction and/or valence bands. Such materials are
charge transfer salts.
The electrical and optical properties of the four
charge-transfer salts formed between the two donors
tetrathiafulvalene (TTF) and
dibenzotetrathiafulvalene (DBTTF) and the two
acceptors tetracyanoquinodimethan (TCNQ) and 2,3dichloro-5,6-dicyano-p-benzoquinone (DDQ ) are
compared. The differences are rationalized on the
basis of electrochemical considerations. DBTTF–
TCNQ, the compound composed of the weakest
donor and acceptor, is found to be a neutral complex.
However, TTF–TCNQ, and the new material
DBTTF–DDQ are mixed valence and highly
conducting. The latter material, which is the first
highly conducting salt to contain the common
acceptor DDQ, has a room temperature pellet
electrical conductivity of 8 Ω−1 cm−1.
Thanks.