Polymers in Special Uses 2-43
Structures similar to muscle fibers have been proposed by researchers in Japan and Italy. They are
based on the property that a conducting polymer in a fiber from undergoes dimensional changes due to
expansion and contraction along the fiber’s length as a result of electrochemical doping and undoping.
Other possible applications include conductive paints, toners for reprographics and printing, and as
components for aircraft where the combination of light weight, mechanical strength, and moderately
high conductivity are required.
Recently, electrically conductive fiber composites have been prepared from polypyrrole-engineered
pulp fibers [58]. To prepare such fibers, FeCl3 solution is first dispersed into pulp, which is disintegrated
by kneading and stirring. The dopant (anthraquinone-2-sulfonic acid, sodium salt) slurry and pyrrole
solution are then added to start the polymerization, the molar ratio of FeCl3 to pyrrole and that of dopant
to pyrrole being 3:1 and 1:3, respectively, for the optimum effect. Paper composites can be prepared both
directly from the modified pulp fibers and by adding the modified fibers as conductive-fiber fillers into
the paper making stock. For the latter method, less monomer (i.e., conductive polymer) is needed to
achieve the same level of conductivity while a higher tensile strength in the paper is attained, as compared
to paper obtained exclusively from treated fibers.
2.4.3 Photoconductive Polymers
The enhanced flow of current under the influence of an applied electric field that occurs when a
semiconductor is exposed to visible light or other electromagnetic radiation is known as photoconduc-
tion. Poly (N-vinyl carbazole) (VII) and various other vinyl derivatives of polynuclear aromatic
compounds such as poly(2-vinyl carbazole) (VIII) and poly(vinyl pyrene) (IX) have high photo-
conductive efficiencies. The excellent photoconductivities of these polymers are believed to be due to
their helical condormation with successive aromatic side chains lying parallel to each other in a stack
along which electron transfer takes place relatively easily.
N N CH CH2 n
CH − CH2 H
n
(VII) (VIII)
O
O2N NO2
NO2
CH − CH2
n
(IX) (X)
Poly(N-vinyl carbazole) absorbs light in the 360 nm region to undergo electronic excitation and
ionization in the electric field. The photogeneration efficiency of the polymer can be greatly enhanced by
the addition of an equimolar amount of 2,4,7-trinitrofluorenone (TNF) (X), which shifts the absorption
of poly(N-vinyl carbazole) into the visible range by the formation of a charge transfer state, rendering it
photoconductive at 550 nm. While the polymer alone is a hole conductor, the addition TNF creates
electron carriers and the conduction mechanism actually becomes electron dominated.
Photoconduction forms the basis of electroreprography. In this photocopying process, or xerography
as it is sometimes known, a photoconductive material is coated onto a metal drum and uniformly
charged (sensitized) in darkness by a corona discharge. The drum is then exposed to the bright image of
Structures similar to muscle fibers have been proposed by researchers in Japan and Italy. They are
based on the property that a conducting polymer in a fiber from undergoes dimensional changes due to
expansion and contraction along the fiber’s length as a result of electrochemical doping and undoping.
Other possible applications include conductive paints, toners for reprographics and printing, and as
components for aircraft where the combination of light weight, mechanical strength, and moderately
high conductivity are required.
Recently, electrically conductive fiber composites have been prepared from polypyrrole-engineered
pulp fibers [58]. To prepare such fibers, FeCl3 solution is first dispersed into pulp, which is disintegrated
by kneading and stirring. The dopant (anthraquinone-2-sulfonic acid, sodium salt) slurry and pyrrole
solution are then added to start the polymerization, the molar ratio of FeCl3 to pyrrole and that of dopant
to pyrrole being 3:1 and 1:3, respectively, for the optimum effect. Paper composites can be prepared both
directly from the modified pulp fibers and by adding the modified fibers as conductive-fiber fillers into
the paper making stock. For the latter method, less monomer (i.e., conductive polymer) is needed to
achieve the same level of conductivity while a higher tensile strength in the paper is attained, as compared
to paper obtained exclusively from treated fibers.
2.4.3 Photoconductive Polymers
The enhanced flow of current under the influence of an applied electric field that occurs when a
semiconductor is exposed to visible light or other electromagnetic radiation is known as photoconduc-
tion. Poly (N-vinyl carbazole) (VII) and various other vinyl derivatives of polynuclear aromatic
compounds such as poly(2-vinyl carbazole) (VIII) and poly(vinyl pyrene) (IX) have high photo-
conductive efficiencies. The excellent photoconductivities of these polymers are believed to be due to
their helical condormation with successive aromatic side chains lying parallel to each other in a stack
along which electron transfer takes place relatively easily.
N N CH CH2 n
CH − CH2 H
n
(VII) (VIII)
O
O2N NO2
NO2
CH − CH2
n
(IX) (X)
Poly(N-vinyl carbazole) absorbs light in the 360 nm region to undergo electronic excitation and
ionization in the electric field. The photogeneration efficiency of the polymer can be greatly enhanced by
the addition of an equimolar amount of 2,4,7-trinitrofluorenone (TNF) (X), which shifts the absorption
of poly(N-vinyl carbazole) into the visible range by the formation of a charge transfer state, rendering it
photoconductive at 550 nm. While the polymer alone is a hole conductor, the addition TNF creates
electron carriers and the conduction mechanism actually becomes electron dominated.
Photoconduction forms the basis of electroreprography. In this photocopying process, or xerography
as it is sometimes known, a photoconductive material is coated onto a metal drum and uniformly
charged (sensitized) in darkness by a corona discharge. The drum is then exposed to the bright image of
