New Electronics With
An experimental OLED-based graphic display
under development at Royal Philips Electronics.
Since the early years
of last century, plastics
have transformed our lives
in numerous ways. Our
modern lifestyle would be
unthinkable without heavy
use of all kinds of different
plastics. While plastics
have a variety of useful
properties, electrical
conduction was not
counted as one of them.
That was until 1986 when
a conducting form of
polyacetylene — a so-called
conjugated polymer —
was discovered.
ELECTRICALLY
CONDUCTING
POLYMERS
◆ by Faiz Rahman
Several other conducting polymers were found in the following years. The common factor
that causes conductivity in all these
materials is the particular form of their
molecular structure. Polymers consist of
long chains of atoms connected to each
other by single, double, or triple bonds.
Organic polymers — which include
plastics — consist of chains of carbon
atoms with other atoms connected to
the central polymer backbone.
In conjugated polymers, carbon
atoms are alternately connected to each
other with single and double bonds. This
type of bonding is called sp2 bonding by
54 June 2006
chemists and is also found in graphite —
a well known electrical conductor. The
reason graphite and conjugated polymers conduct electricity is because an
alternating arrangement of carbon-carbon bonds causes one electron per
carbon atom to be very weakly bonded
to the polymer chain. All such electrons
are able to roam around freely in one
(polymers) or two (graphite) dimensions
and are called itinerant electrons. This
then causes end-to-end conduction in
electronic polymers and graphite, as
seen in Figure 1.
However, because any bulk sample of a conjugated polymer consists
of chains only a few microns long that
don’t span its entire length, such
samples don’t show strong signs of
electrical conductivity. Bulk electrical
conduction is seen, however, when
these polymers are doped with
electron or hole donating agents. The
excess carriers produced this way can
jump from chain to chain producing
sample-wide electrical conductivity.
Like all polymers, conducting
polymers, too, can be easily
processed into various shapes. A large
application area is in coatings for corrosion prevention of ferrous metals,
electrostatic discharge prevention for
