Transcript Substantially Conductive Polymers

Substantially Conductive
Polymers
Part 07
Applications of PPV
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Due to its stability, processability, and electrical and optical properties, PPV has been considered for
a wide variety of applications.[1]
In 1989 the first polymer-based light emitting diode (LED) was discovered using PPV as the emissive
layer.[3] Polymers are speculated to have advantages over molecular materials in LEDs, such as ease
of processing, reduced tendency for crystallization, and greater thermal and mechanical stability.
Ever since the first breakthrough in 1989, a large number of PPV derivatives have been synthesized
and used for LED applications. Although solid-state lasing has yet to be demonstrated in an organic
LED, poly[2-methoxy-5-(2’-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) has been proven to be
a promising laser dye due to its high fluorescence efficiency in solution.[4]
Polyphenylene vinylene is capable of electroluminescence, leading to applications in polymerbased organic light emitting diodes. PPV was used as the emissive layer in the first polymer lightemitting diodes.[5]
Devices based on PPV emit yellow-green light, and derivatives of PPV obtained by substitution are
often used when light of a different color is required. In presence of even a small amount of
oxygen, singlet oxygen is formed during operation, by energy transfer from the excited polymer
molecules to oxygen molecules. These oxygen radicals then attack the structure of the polymer,
leading to its degradation. Special precautions therefore have to be kept during manufacturing of
PPV in order to prevent oxygen contamination.
PPV is also used as an electron-donating material in organic solar cells.[6] Although PPV-based
devices suffer from poor absorption and photodegradation, PPV and PPV derivatives (especialy
MEH-PPV and MDMO-PPV) find frequent application in research cells.[7]
Polypyrrole
• A conjugated polymer based on heterocyclic
aromatic units on the main chain
• Synthesized by chemical or electrochemical
polymerization from pyrrole
• Mechanism: oxidative coupling reaction
Proposed mechanism for the electrochemical polymerization
Polythiophene
• Environmental stable and highly
resistant to heat
• Synthesized by the electrochemical
polymerization of thiophene
• Can also be obtained by various types
of metal catalyzed coupling reaction
The solubility and processibility can be enhanced by attaching
substitution groups at the 3 position
However, the coupling can be either head-to-head (HH), headto-tail (HT), or tail-to-tail (TT)
Synthesis of Regioregular Polythiophene
Copolymers with aromatic compounds or vinylene group
Conductivity of polythiophenes and
polypyrroles doped under different conditions
Material
Dopant
s (S cm-1)
Polythiophene
Poly(3-methylthiophene)
Poly(3-ethylthiophene)
Poly(3-buthylthiophene)
Poly(3-hexylthiophene)
Poly(3-hexylthiophene)
SO3CF3PF6PF6I2
PF6I2
10-20
510
270
4
30
11
Polypyrrole
Polypyrrole
Polypyrrole
Polypyrrole
FeCl3
I2
Br2
Cl2
3-200
2-8
5
0.5
Applications of PT
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A number of applications have been proposed for conducting PTs, but none has been
commercialized.
Potential applications include field-effect transistors,[74] electroluminescent devices, solar cells,
photochemical resists, nonlinear optic devices,[75] batteries, diodes, and chemical sensors.[76]
In general, there are two categories of applications for conducting polymers. Static applications
rely upon the intrinsic conductivity of the materials, combined with their ease of processing and
material properties common to polymeric materials. Dynamic applications utilize changes in the
conductive and optical properties, resulting either from application of electric potentials or from
environmental stimuli.
As an example of a static application, poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate)
(PEDOT-PSS) product Clevios P (Figure) has been extensively used as an antistatic coating (as
packaging materials for electronic components, for example). AGFA coats 200 m × 10 m of
photographic film per year with Clevios because of its antistatic properties. The thin layer of Clevios
is virtually transparent and colorless, prevents electrostatic discharges during film rewinding, and
reduces dust buildup on the negatives after processing.
PEDOT can also be used in dynamic applications where a potential is applied to a polymer film. The
electrochromic properties of PEDOT are used to manufacture windows and mirrors which can
become opaque or reflective upon the application of an electric potential.[27] Widespread adoption
of electrochromic windows could save billions of dollars per year in air conditioning costs.[77] Finally,
Phillips has commercialized a mobile phone with an electrically switchable PEDOT mirror
Polyaniline
• A conducting polymer that can be grown
by using aqueous and non-aqueous route
• Can be obtained by electrochemical
synthesis or oxidative coupling of aniline
• Doping achieved by adding protonic acid
• Several forms: leucoemaraldine,
emaraldine, emaraldine salt,
pernigraniline
Electrical Conductivity
Medium
s (S cm-1)
5-Sulfosalicyclic acid
Benzene sulfonic acid
p-Toluene sulfonic acid
Sulfamic acid
Sulfuric acid
0.2-1.0
2.0
5.0
2.0
1.2
Applications of PANI
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Polyaniline and the other conducting polymers such as polythiophene, polypyrrole, and
PEDOT/PSS have a great deal of potential for applications due to their light weight,
conductivity, mechanical flexibility and chemical properties.
Polyaniline is especially attractive among them because it is less expensive, has three distinct
oxidation states with different colors and has an acid/base doping response.
This latter property makes polyaniline an ideal option for acid/base chemical vapor sensors.
The different colors, charges and conformations of the multiple oxidation states also make the
material highly promising for applications such as actuators, supercapacitors and
electrochromics.
Attractive fields for current and potential utilization of polyaniline is in antistatics, charge
dissipation or electrostatic dispersive (ESD) coatings and blends, electromagnetic interference
shielding (EMI), anti-corrosive coatings, hole injection layers[12], transparent conductors, ITO
replacements, actuators, chemical vapor and solution based sensors, electrochromic coatings
(for color change windows, mirrors etc.), PEDOT-PSS replacements, toxic metal recovery,
catalysis, fuel cells and active electronic components such as for non-volatile memory.
However, the major applications are in printed circuit board manufacturing (final finishes)
and corrosion protection.
Commercially polyaniline has been supplied by several companies PANIPOL, Eeonyx, Fibron
Technologies Crosslink and Ormecon.
ELECTROPOLYMERIZATION
Electropolymerization
Schematic of a typical electrochemical
experiment used to probe conjugated polymer
and oligomer electrochemistry
Repeated cycling
electropolyermization
by cyclic voltammetry.
The inset is of the first
CV scan showing the
oxidation of the
monomer.