conducting polymers 4

7/25/2019 Conducting Polymers 4

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Conducting Polymers

Master in Nanoscience

Low dimensional system and nanostructures

January 2009

Yasmin Khairy Abd l !atah


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"#$L%N

%ntroduction

&hat is conducti'ity(

&hat ma)es amaterial conducti'e(

*ow can +lastic become conducti'e(

,o+ing +rocess-

.actors that a!!ect the conducti'ity-

A++lications-Conclusion-

/ibliogra+hy search-


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%ntroduction

Polymers or +lastics as they are also called1 are

)nown to ha'e good insulating +ro+erties-

Polymers are one o! the most used materials in the modernworld- $heir uses and a++lication range !rom containers to

clothing-$hey are used to coat metal wires to +re'ent electric shoc)s-


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Yet Alan J- *eeger Alan 3- Mac,iarmid and *ide)i 4hira)awa ha'e

changed this 'iew with their disco'ery that a +olymer +olyacetylene

can be made conducti'e almost li)e a metal-


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What is conductivity?

Conducti'ity can be de!ined sim+ly by "hms Law-

56 %7&here 7 is the resistance % the current and 5 the'oltage+resent in

the material- $he conducti'ity de+ends on the number o! chargecarriers number o! electrons1 in the material and their mobility-%n ametal it is assumed that all the outer electrons are !ree to carrycharge and the im+edance to !low o! charge is mainly due to theelectrons 8bum+ing8 in to each other-

%nsulators howe'er ha'e tightly bound electrons so that nearly no

electron !low occurs so they o!!er high resistance to charge !low-

4o !or conductance !ree electrons are needed-
http://www.chm.bris.ac.uk/webprojects2001/parrott/pages/resistance.htmhttp://www.chm.bris.ac.uk/webprojects2001/parrott/pages/voltage.htmhttp://www.chm.bris.ac.uk/webprojects2001/parrott/pages/voltage.htmhttp://www.chm.bris.ac.uk/webprojects2001/parrott/pages/resistance.htm


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&hat ma)es the material conducti'e(

$hree sim+le carbon com+ounds are diamond gra+hite and+olyacetylene- $hey may be regarded as three two and onedimensional !orms o! carbon materials -

,iamond which contains only : bonds is an insulator

and its high symmetry gi'es it isotro+ic +ro+erties-

3ra+hite and acetylene both ha'e mobile ; electrons

and are when do+ed highly anisotro+ic metallic

conductors-


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*ow can +lastic become conducti'e(

Plastics arepolymers molecules that !orm long chains re+eating

themsel'es- %n becoming electrically conducti'e a +olymer has to

imitate a metal that is its electrons need to be !ree to mo'e and

not bound to the atoms- Polyacetyleneis the sim+lest +ossible

con


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$wo conditions to become

conducti'e=

>$he !irst condition !or this is that the +olymer consists o! alternating

single and double bonds called con


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2$he second condition is that the +lastic has to be disturbed either by remo'ing electrons !rom oidation1 or insertingthem into reduction1 the material- $he +rocess is )nown as

Doping.$here are two ty+es o! do+ing=

>oidation with halogen orp-do+ing1-

2 7eduction with al)ali metal called ndo+ing1-

( ) ( ) + ++ xNaCHxNaCH xnn

( ) ( ) + ++3

2

3ICHI

xCH

nn


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$he game o!!ers a sim+le model o! a do+ed +olymer- $he +iecescannot mo'e unless there is at least one em+ty 8hole8- %n the+olymer each +iece is an electron that


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,o+ing +rocess

$he halogen do+ing trans!orms +olyacetylene to a good conductor-

"idation with iodine causes the electrons to be


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$he iodine molecule attracts an electron !rom the

+olyacetylene chain and becomes %B- $he +olyacetylene

molecule now +ositi'ely charged is termed a radical cationorpolaron.

D $he lonely electron o! the double bond !rom which an

electron was remo'ed can mo'e easily- As aconseEuence the double bond successi'ely mo'es along

the molecule-D $he +ositi'e charge on the other hand is !ied by

electrostatic attraction to the iodide ion which does not

mo'e so readily-


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,"P%N3 ."7 /$$7

M"LC#L P7."7MANC

Doped polyacetylene is, e.g., comparable to good conductors

such as copper and silver, whereas in its original form it is a

semiconductor.

Conductivity of conductive polymers compared to those of other

materials, from quartz (insulator to copper (conductor. !olymers

may also have conductivities corresponding to those of

semiconductors.


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.actors that a!!ect the conducti'ity

>,enesity o! charge carriers-

2 $hier mobility-

B$he direction-F+resence o! do+ing materials

additi'es that !acilitate the +olymer

conducti'ity1G$em+erature-


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The conductivity of conductive polymers decreases with falling

temperature in contrast to the conductivities

of typical metals, e.g. silver, which increase with fallingtemperature.


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A++lications

Conducting +olymers ha'e many uses- $he most documented

are as !ollows=antistatic substances !or +hotogra+hic !ilm

Corrosion %nhibitors

Com+act Ca+acitors

Anti 4tatic Coating

lectromagnetic shielding !or com+uters84mart &indows8

A second generation o! conducting +olymers ha'e beende'elo+ed these ha'e industrial uses li)e=

$ransistors

Light mitting ,iodes L,s1

Lasers used in !lat tele'isions4olar cells

,isplays in mobile telephones and mini"formattelevision screens


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Photogra+hic .ilm

smart8 windows

4hield !or com+uter screen

against electromagnetic

8smart8 windows

radiation

Lightemitting diodes

4olar cell


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Conclusion

.or conductance !ree electrons are needed-

Con


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/ibliogra+hic 4earch

#. $hira%awa, &.'. ouis, ).*. +acDiarmid, C.. Chiang and ).'.

#eeger, ' Chem $oc Chem Comm (-// 0/

1. 2to, #. $hira%awa and $. 2%eda, '.!olym.$ci.,!olym.Chem. &d. -3

(-/4 --536

C.. Chiang, C.7. 8ischer, 9.W. !ar%, ).'. #eeger, #. $hira%awa, &.'.

ouis, $.C. *au and ).*. +acDiarmid , !hys. 7ev. etters : (-//

-6;C.. Chiang, +.). Druy, $.C. *au, ).'. #eeger, &.'. ouis, ).*.

+acDiarmid


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conducting polymers 4

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