a) b - École Polytechnique de Montréal

different from that of linear homopolymers(Stratouras & Kosmas, 1992; Van Lent, Scheutjens,
& Cosgrove, 1987). As mentioned before, due to the increase of polymer concentration close to
the surface, polymer chains adsorb to the substrate. In an adsorption process of a linear
homopolymer, all monomers have the same interaction with the substrate, but some
distinguished sections of adsorption are still observed (Figure 2-37). An adsorbed single polymer
chain can be divided into three sections, consisting of trains, which are monomers bound to the
surface, loops, which are a number of unattached monomers between trains, and tails, which are
end sections that can form dangling sections.
Figure 2-37. The ‘tail’, ‘train’ and ‘loop’ sections of the adsorbing chain
2.4.1.1.3 Adsorption of Polyelectrolytes on the Surface of a Substrate
Generally, there are two factors determining adsorption behavior for a neutral polymer chain.
The first factor is reduction of conformational states of the polymer at the substrate. The second
one is substrate-monomers interactions(Israelachvili, 1992) that depend on the solvent, the
chemical nature of the monomer, and the substrate material. Attractive or repulsive van der
Waals interactions exist between the substrate and polymer monomers. It is observed that for
strongly attractive potentials or low temperatures, the adsorption between polymer and surface is
very strong and the thickness of the adsorbed layer is small (Figure 2-38a). Conversely, at high
temperatures or if the attractive potentials are weak, a weakly adsorbed layer is anticipated while
a diffuse layer thickness, much larger than in the previous case, is observed (Figure 2-38b).
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