Chemistry Reference
In-Depth Information
Conductive fibres obtained through chemical deposition
of coatings
Chemical deposition of different polymers, such as polyaniline, polypyrrole
and polythiophene that possess conductive properties is obtained through
deposition of the monomer followed by polymerisation in the presence of
an initiator (e.g. FeCl
3
). In this method, the surface to be coated is enriched
either with a monomer, or an oxidising agent (through spontaneous depo-
sition, using auxiliary reagents that promote the adsorption), followed by
treatment with a solution of either oxidising agent or monomer, respec-
tively. A major advantage of this process is that the polymerisation occurs
almost exclusively at the surface, and there is no bulk polymerisation in the
solution. The enrichment of the surface by an oxidiser can occur either by
ion-exchange mechanism, or by the deposition of an insoluble layer of oxi-
diser. The process is limited by materials that can be covered or enriched
with a layer of either monomer or oxidiser in a separate stage, preceding
the surface polymerisation
46-51
.
An alternative to chemical polymerisation for coating is electro-
polymerisation of monomers at electrodes performed either in aqueous, or
in organic solutions. However, electro-polymerisation is strongly restricted
by the use of conducting materials because an activation potential needs to
be applied, and an electrical current should be able to flow in the electrodes.
This implies that the initial fibre to be coated should already have conduc-
tive properties which limits the use of this method
52
.Frequently, electro-
polymerisation is used as a finishing touch after fibres have been treated
with a chemical deposition, the latter providing the conductive properties
to the fibre necessary to perform electro-polymerisation.
Spraying a solution containing the polymer onto the surface of a textile,
followed by solvent evaporation, is an alternative method, but is not
discussed here because of its poor reproducibility, poor adhesion of the
polymer to the substrate, inhomogeneous distribution of the polymer on
the fibre surface, large fluctuations in layer thickness and co-deposition of
impurities present in the solution
53
. Another method, also limited in use, is
bulk polymerisation of the monomer to form insoluble polymers, which
precipitate on the surface of the fibres. In this case, it is the insolubility of
the polymer that is the driving force for precipitation and not the strength
of the bonding and type of bonding (adsorption, covalent bonding) that
determines the stability of the deposited polymer onto the fibre. A strong
bonding is not necessarily obtained, and this could seriously limit the
possible applications of such a modified fibre
54-66
.
8.4.3
The electrotextile challenges
Textiles offer a unique combination of attributes to facilitate the fabrica-
tion of electrotextile systems. They are lightweight, flexible and con-
