a) b - École Polytechnique de Montréal

APPENDIX III
A- 3 Mechanism of Aggregation of Weak Polyelectrolytes
Weak polyelectrolytes have some advantages compared to strong ones, such as the possibility of
tuning their properties by simple pH adjustment. In strong polyelectrolytes, the charges remain
over the entire pH range. On the contrary, for weak polyelectrolytes, the degree of ionization
depends on the pH of the solution. In this thesis, the pH of polyaniline solution is set constant at
2.5 for all samples in order to have the equal fraction of charges for layers. Moreover, the weak
PANI shows a “poor” nature in aqueous solutions(Cheung, et al., 1997). Such poor solvent
quality indicates that the polyaniline solution can only be used for about 1-2 weeks before
important aggregation of the polyaniline chains happens(Cheung, et al., 1997). In this case, a
large amount of polymer chains is adsorbed per layer and multilayer deposition cannot be
controlled. The aggregation of polyelectrolytes in a solution throughout layer-by-layer
experiments was studied over time for sample B in Chapter 5 in two steps (Figure A-3.1). In the
first continuous process, 22 layers were deposited onto the 3D substrate. After the deposition of
the 22 nd layer, all the solutions were left for three weeks to allow the chains to make aggregates.
The second LbL process was continued by the same solutions and substrates, whereas layers 23
to 37 were deposited on the previously prepared multilayer. In this protocol, two different growth
rates of deposition of NaPSS for either step were obtained. The deposition process with fresh
solutions exhibited a growth rate of 3.04, while a higher growth rate value of 6.27 was obtained
for the remaining sample. Such a high growth rate demonstrates the aggregation deposition of
chains in the second step instead of the deposition of a few chains in the first step.
Correspondingly, a solution containing fresh PANI shows a rate of desorption of 2.28, compared
to the solution used in the second step with a rate of 5.22. The aggregation of PANI resulting
from the poor nature of the PANI solution is proposed as the main reason for the increase of the
growth and desorption rates. Therefore, in the second step, a large number of aggregated PANI
chains was deposited, yielding a significant increase in electrostatic force. In the subsequent
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