a) b - École Polytechnique de Montréal

2.4.1.1 Fabrication of Conductive Multilayers by the LbL Method
Conducting polymers prepared by thin film technology have become increasingly important for
electrical and optical applications. Polyaniline is one of the most promising electrically
conducting polymers due to ease of synthesis, versatile processability, stable electrical
conductivity, and relatively low cost. PANI is used in a wide variety of fields such as chemical
sensors(Dan, Yadong, Zhiming, Xiangdong, & Yanrong, 2000; Mathur, Misra, Singh, &
Tripathi, 2002), solar cells, light-weight batteries, light emitting diodes, polymer actuators, and
corrosion protection agents. Shirakawa et al.(Ito, Shirakawa, & Ikeda, 1974) found that by
“doping” polyacetylene, its conductivity is increased by many orders of magnitude. There are
two kinds of dopants: electron acceptors (p-type dopants) such as iodine, and electron donors (n-
type doping). The use of various concentrations of dopants can vary electrical properties by as
much as 18 orders of magnitude, and so conductivity can be controlled in a wide range. The
conductivity of the emeraldine base (EB), which is the best representation of polyaniline at
ambient temperature, is about 10 -10 S/cm, while by doping it with different acids and adding sites
of (-N=) to EB, emeraldine salt can be formed with a conductivity of about 5 S/cm at the same
temperature(Epstein et al., 1986; Ginder, Richter, MacDiarmid, & Epstein, 1987). Ferreira et
al.(Ferreira, Cheung, & Rubner, 1994) found that both aqueous and polar organic solutions of
positively charged protonated forms of polyaniline and polypyrrole can be prepared, although
solubility of PANI in an organic medium such as dimethylacetamide(DMA) is much higher than
that in water. Nevertheless, for LbL self assembly, preferred media are aqueous solutions.
The preferential affinity of certain ions for others is an important factor in film growth. In low
molar mass compounds, chloride or bromide bind much stronger to the ammonium group than
sulfonate does and sodium binds stronger to the sulfonate group than to chloride and bromide.
For example, film growth forms smoothly using sodium poly(styrene sulfonate) and poly(N,N,Ntrimethyl-2-methacryloylethyl
ammonium) bromide or poly(diallyldimethyl-ammonium)
chloride(Bertrand, 2000).
Rubner’s group at MIT investigated both electrostatic and hydrogen-bonded LbL assembly using
fully and non-fully ionized polyelectrolyte in solution. They found that the structure of
polyelectrolyte multilayer depends on the degree of ionization of the polyelectrolyte. They
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