a) b - École Polytechnique de Montréal

The percolation threshold of PANI in this porous device is achieved at a maximum of 8 layers.
This corresponds to 0.19 wt.% PANI for sample A and 0.28 wt.% for sample B. The
conductivity saturation plateau is achieved at 32 layers which corresponds to 0.76% PANI for
sample A and 1.1% for sample B. This dependence of conductivity on deposited layers confirms
the hypothesis that deposited PSS and PANI form a network type construction as opposed to the
formation of discrete PSS and PANI layers. In fact, this network formation allows for the fine
tuning of conductivity over several orders of magnitude. Clearly, the deposition of only a few
layers results in an incomplete network with disconnections in many parts and demonstrates a
limited passage of electricity and thus yields a low conductivity value. By increasing the number
of layers to 8 and 16, higher conductivity values are obtained and the conductivity is in the 10 -9 -
10 -8 S cm -1 range. As more PANI chains are added they diffuse into the network resulting in a
significant increase in network branches. The addition of further layers results in a plateau value
for conductivity at approximately 10 -6 S cm -1 for sample A and 10 -5 S cm -1 for sample B. Beyond
32 layers, the further addition of PANI has no effect on the conductivity of the device. The
conductivity of sample C and D after the deposition of 38 PSS/PANI layers was measured
showing the values of 10 -9 S cm -1 and 3×10 -7 S cm -1 respectively. The difference in the
conductivity values can be dependent on several factors such as pore sizes and pore distribution;
however the most important one is the internal surface area of the substrate.
The addition of salt during the LbL process has little influence on the conductivity of the sample
as shown in Figure 5-10. Braga et al. (Braga, et al., 2008) and Paloheimo et al.(Paloheimo, et al.,
1995) reported that the electrical resistance of PANI/PSS layers with solutions of different
polymer concentrations decreases as more layers are adsorbed until a saturation plateau is
reached, between the 26 th and 30 th layer. This closely corresponds with the results observed in
this work. It is very likely that the formation of a diffuse network structure in the current study is
critical in obtaining high conductivity values. Discrete molecular layers added in a classic LbL
protocol using strong polyelectrolytes would have likely resulted in a lower percolation threshold
value, but also would not be capable of achieving the high conductivities observed at saturation
as seen in this study.
166