CONDUCTIVE PLASTIC by nikeborome

VIEWS: 27 PAGES: 22

									 CONDUCTIVE
   PLASTIC
Prepared By :
          CONTENTS
INTRODUCTION
RELEVANT PHYSICS
THE POLYLED
POPERTIES
APPLICATION IN VARIOUS FIELDS
LIMITATION
CONCLUSION
REFERENCE
      INTRODUCTION
Plastics are polymers, that is chains of many
identical molecules (monomers) that are
intercoupled. The reason that most plastics are
isolators is that their electrons are localized.
Each electron is firmly fixed, as it were, to its
own atomic nucleus. This means that the
electrons, carriers of the electric current, cannot
move freely in the material. Conductive or
semiconductive plastics, were discovered in
Japan in1977. In these, the polymer chains have
conjugated connections i.e. the discrete atoms
are interconnected alternately by a single and a
double chemical bond.
    RELEVANT PHYSICS
Conductive or semi conductive plastics are polymer
chains with conjugated double links. The first PolyLEDs
werebased on polyphenyl-vinyl (PPY). The principle of
their conductivity (or, rather semiconductivity) is best
illustrated by the simplest polymer with a conjugated
structure: polyacetylene. See Figure.
The single bond in the conjugated structure is always a
a-bond, whereas the double one consists of a a-bond
and a n-bond, which has a different character. Two
variants of poIyacetylene that differ only in the locations
of the n-bonds are shown in Figure. These variants could
be merged freely. The real structure is a mixture of the
variants in which each is represented equally. This has
an important consequence: in the case of an a-bond, the
electrons forming the bond are bonded to both nuclei
and therefore localized. Normally, this is also the case
with electrons ,forming a n-bond. Because of the
conjugated structure, that is, a mixture , the electrons
are free to move along the entire chain.
This does not mean, of course, that the
material itself, which consists of many
monomers, becomes conductive. This
occurs only when electrons can hop from
one chain of polymers to another. It has
been found that this becomes possible
when the chains are in close proximity of
each other. The closer the chains are
together, the more mobile the electrons
become. This is further enhanced by
purification of the material and doping it,
that is, adding charge carriers.
          THE POLYLED
When an electric potential is applied across semi
conductive plastics, they emit light. This forms
the basic of PolyLED.
The PolyLED is essentially a much simpler
component than a transistor. Its applications
include segment displays such as used in
mobile telephones and background lighting in
liquid-crystal displays.
PolyLEDs operate with low (battery) voltage and
are therefore eminently suitable for use in
modern equipment.
         PROPERTIES
Steadily increasing the length of a purified
conducting polymer vastly improves its ability to
conduct electricity, Their study of regioregular
polythiophenes (RRPs) establishes benchmark
properties for these materials that suggest how
to optimize their use for a new generation of
diverse materials, including solar panels,
transistors in radio frequency identification tags,
and light-weight, flexible, organic light-emitting
displays .
Unlike plastics that insulate, or prevent, the flow
of electrical charges, conducting plastics actually
facilitate current through their nanostructure.
Conducting plastics are the subject of intense
research, given that they could offer light-weight,
flexible, energy-saving alternatives for materials
used in solar panels and screen displays. And
because they can be dissolved in solution,
affixed to a variety of templates like silicon and
manufactured on an industrial scale, RRPs are
considered among the most promising
conducting plastics in nanotech research today.
   Mobility of electrons increases exponentially
as the width of a nanofibril increases, Each rope-
like nanofibril actually is a stack of RRP
molecules, so the longer these molecules, the
wider the nanofibril and the faster the electrical
conductivity. In this way, electricity moves
preferably perpendicular through the rows of
naturally aligned nanofibrils.
 Charge carriers encounter fewer hurdles when
jumping between wider nanofibrils. So the
nanostructure of our conducting plastic
profoundly enhances its ability to conduct
electricity
                APPLICATION
                  Electrical application



1.    BRUSHLESS MOTOR             2. D.C. MOTOR




3.   D.C. TORQUE POTENTIOMETER   4. D.C. TORQUE MOTOR
ELECTRONICS
APPLICATION
     Keypads



     Phosphorescent rubber
       keypads

     Rubber keypads
Batteries
  In an age of massive portability in electronics,
the need for improved batteries is critical. There
is a tremendous growth in laptop computers,
cellular phones and personal digital assistants
(PDAs). Electronics are being put in every place
therefore, replacing heavier metal components
with lightweight polymers would seem to be
highly desirable.
  The electrodes of all common batteries are
made of metals. (Car batteries are lead,
flashlight batteries are nickel/cadmium, and
button cells are lithium.) By replacing these
metals with conductive polymers, the following
advantages have been shown: lower weight,
lower cost, more charge/discharge cycles, lower
toxicity, and improved recyclability.
Light-Emitting Diodes
 Conductive polymers have been made into
devices that provide an alternative to
conventional backlit LCD displays. The devices
termed OLEDs(organic light-emitting diodes),
which use conductive polymers, are sandwich-
type structures where the active polymeric film
layer is positioned between a semi-transparent
anode and a back row cathode. The devices
emit uniformly over the entire device. Such
devices are applied in displays for cellular
telephones, camcorders, PDAs, and numerous
industrial devices needing a readout display.
Their present advantages over LCD backlit
displays include lower power, lighter weight,
increased durability (no glass), wider viewing
angle, and increased brightness; their future
advantage of lower cost is also promising.
Microtool
 One interesting property of many conductive
polymers is that they swell when they conduct.
This means that conductive polymers can
change electrical signals into mechanical
energy, similar to piezoelectric materials.
However, in contrast to piezoelectric films,
conductive polymeric films work well at low
voltages, thus expanding the areas of
applicability for such devices.
     MEDICAL APPLICATION
    Medical applications under evaluation or
    currently using conductive thermoplastics
    include:
1. Bodies for asthma inhalers. Because the
    proper dose of asthma medications is critical to
    relief, any static "capture" of the fine-
    particulate drugs can affect recovery from a
    spasm.
2. Airway or breathing tubes and structures. A
    flow of gases creates triboelectric charges,
    which must discharge or decay. A buildup of
    such charges could cause an explosion in a
    high-oxygen atmosphere.
3. Antistatic surfaces, containers, and packaging to
    eliminate dust attraction in pharmaceutical
    manufacturing.
4.ESD housings to provide Faraday cage
  isolation for electronic components in
  monitors and diagnostic equipment.
5.EMI housings to shield against
  interference from and into electronics.
6.ECG electrodes manufactured from highly
  conductive materials. These are x-ray
  transparent and can reduce costs
  compared with metal components.
7.High-thermal-transfer and microwave-
  absorbing materials used in warming fluids
           LIMITATION
Conductive polymers do not conduct electricity
at the same speed as silicon chips. Polymers
are, therefore, limited to those applications
where gross or relatively slow changes occur.

The conductive polymers are still much weaker
in mechanical strength when compared to
metals, although the polymers are better than
silicon-based devices. Also, the polymer
materials are softer and therefore, more likely to
be damaged by scratching and abrasion when
compared to metals.
Lastly, polymeric devices are mostly conductive
in only one or two dimensions, whereas metals
are fully conductive in three dimensions; that is,
they are anisotropic conductors. The
dimensionality restriction of the polymers
(anisotropy) is because polymers are linear or,
occasionally, planar structures, and the
delocalized electrons follow the shape of the
polymer network. Designers need to be aware of
this difference in directional conductivity. It can
be a problem but, in some applications, it might
also be an advantage to have a significantly
reduced conductivity in a specific direction. In
fact, anisotropic conductors are used in many
applications in electronics, including inexpensive
digital watches
           CONCLUSION
Surely conductive polymers are exciting developments.
As they become more common, they have become part
of many products with which we are already familiar and
will certainly enable many advances in future products.
Some researchers have embarked on a study of
conductive polymers as a new method for storing
electronic information, perhaps optically. These could be
developed into very fast storage and retrieval devices.
Others see conductive polymers as light-detecting
devices that could be configured into large arrays for
military and commercial applications .
       REFERENCES
De Gaspari, John, “New alternatives In
Conductive Plastics,” Plastics Technology,
November 1997, p. 13-15.
Moore, Samuel K., “Just One Word—
Plastics,” IEEE Spectrum, September
2002, p. 55-59.
www.google.com

								
To top