a) b - École Polytechnique de Montréal

close together. It is interesting to note in Figure 5-7 that the addition of salt significantly
increases the oscillation behavior of the mass growth dynamics.
This oscillation behavior can be explained as follows: the number of PSS molecules that diffuse
throughout the multilayer and the total concentration of these free chains depend on the
electrostatic interaction forces that arise from total overcompensation. Two important parameters
influencing the extent of overcompensation are the concentration of added salt and the number of
layers. Thus, extra overcompensation is caused by the presence of NaCl in the PSS
solution(Klitzing & Moehwald, 1995). As well, the displacement of hydrated small salt counterions
and charged polymer segments result in highly swollen polymers as attached water
molecules are brought in(Dubas & Schlenoff, 2001c). Jaber et al. (Jaber & Schlenoff, 2007)
showed that salt counter-ions can thermodynamically control up to 40% of the mass deposition
of the multilayer construction due to this additional water content. Swelling and
overcompensation occur simultaneously during the construction of the multilayer in the presence
of salt(Dubas & Schlenoff, 2001b), which is involved in the dramatic mass increase of the
multilayer.
In a subsequent dipping step in the PANI solution, the electrostatic interaction between the
diffused hydrated PSS with PANI chains inside the solution play a major role in the diffusion of
free PSS chains out of the multilayer. At this step, in the presence of salt, a significant decrease
in mass deposition is detected which is proportional to the mass increase in the previous
step(PSS adsorption) as compared to a slight decrease in mass in solutions without salt.
Consequently, the amount of thickness growth highly depends on the amount of salt that affects
the electrostatic interactions and increases the driving force for diffusion in and out of the
multilayer.
Mass deposition growth for the PSS/PANI system in cases where salt is both present and absent,
is not linear since a progressive increase of each polyelectrolyte after its deposition is detected
(Figure 5-9). As the number of layers increases, the extent of free chains going inward and
outward increases exponentially due to increase the amount of overcompensation (Figure 5-9). In
other words, at each adsorption step, more PSS is adsorbed than that removed in the previous
step, leading to nonlinear layer growth. The rates of increase and decrease of PSS and PANI at
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