Conductive Plastic2

CONDUCTIV E PLASTIC Presented by Nicha Tangha Elect.Engg 7th sem ,03/273

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 ropelike 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.

3.

BRUSHLESS MOTOR

D.C. TORQUE POTENTIOMETER

2. D.C. MOTOR

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 sandwichtype 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 microwaveabsorbing 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