a) b - École Polytechnique de Montréal

on the previously formed layer, establishing a larger structure. At this step, while most of the
PLL chains have diffused out onto the surface, free mobile PGA chains present in the solution
start to diffuse into the multilayer. This time, charge overcompensation is the result of an excess
amount of PGA chains in solution. Again, free PGA chains diffuse out, and these processes
repeat themselves alternately, resulting in a continuous film reconstruction and leading to an
increase in the thickness of the multilayers. Part of the free chains of either polyelectrolyte come
out during the rinsing step with a free aqueous solution. The increase of thickness at each step is
proportional to the mass of PGA/PLL complexes that form on the surface of the multilayer,
which are proportional to the free mobile PLL or PGA chains with weak bonds, that can easily
diffuse out of the film.
a)
Figure 2-43. Penetration of polyelectrolyte chain inward and outward of a multilayer film
Some other polyanion/polycation systems showing linear evolution in thickness increment
generate denser multilayer structures and avoid polyelectrolyte diffusion inside the film. Two
b)
f) e) d)
c)
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