a) b - École Polytechnique de Montréal

Polymers have long been thought of and applied as insulators. Moreover, some observed
electrical conduction in polymers was generally regarded as an undesirable phenomenon. With
the discovery in 1960 of intrinsically conducting polymers (ICPs), a new class of electronically
conducting polymers in the partially oxidized state was surprisingly discovered. In metals and
semiconductors such as silicon, free electrons and holes are the charges that are responsible for
the current. The Nobel Prize in Chemistry in 2000 “for the discovery and development of
electronically conductive polymers” was received by Alan J. Heeger, Alan J. MacDiarmid and
Hideki Shirakawa(Chiang, Druy, et al., 1978; Chiang et al., 1977; Chiang, Park, et al., 1978).
2.3.1 Electrically Conductive Polymers and Composites
Generally, four types of electrically conductive polymer system with different degrees of
conductivity have been recognized(Wise, Wnek, Trantolo, Cooper, & Gresser, 1997).
1. The most widely used conducting polymeric systems where an insulating polymer matrix
is filled with particulate or fibrous conductive fillers such as metal powder, carbon black, or
carbon nanotubes to impart high conductivity.
2. Ionically conducting polymers are electrically conductive because of the movement of
ions present in the system. For example mobility of lithium ions in polyethylene oxide is behind
the electrical conductivity in this system.
3. Redox polymers containing immobilized redox centers (electroactive centers) can
conduct charge by electron transfer from one center to another through the well known
“hopping” mechanism. During conduction, electrons tunnel from one redox center to another
through an insulating barrier. The systems need to have a large number of redox centers to
increase the probability of such tunneling.
4. Intrinsically conducting polymers are conjugated polymers consisting of alternating
single and double bonds, creating an extended π-network. The movement of electrons within this
π-framework is the source of conductivity. However, dopant is required to increase the level of
conductivity for this type of polymers.
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