a) b - École Polytechnique de Montréal

Addition of salt to the solution of polyelectrolyte will cause screening of the charges and
collapse of the rod polyelectrolyte chain occurs, favoring a more conventional conformation,
essentially identical to a neutral chain in good solvent. Another way to control the charge of each
monomer for weak polyelectrolytes, including polyacids and polybases, is adjusting the pH of
the solution. Consequently, it is concluded that due to chain stiffness and electrostatic repulsion
between monomers in a polyelectrolyte, the effective persistence length is increased compared to
uncharged polymers. Figure 2-35 shows a schematic view of the four scaling ranges in a
Gaussian-persistent regime for a polyelectrolyte structure.
As seen, on scales as small as a Gaussian blob of size Rel, each blob contains a segment of length
Lel. Within these blobs, electrostatic interactions are not so effective. Chain stiffening is caused
because of electrostatic repulsions on larger length scales. On a scale larger than Rel, Gaussian
(electrostatic) blobs are aligned linearly due to electrostatic repulsion.
2.4.1.1.2 Polymer Adsorption on the Surface
The choice of substrates has so far been dominated by their convenience for particular analytical
methods. Glass and quartz, because of their transparency, are the most suitable materials for
utilization of optical microscopy and UV-spectroscopy. Silicon wafer enables X-ray reflectivity
studies, ellipsometric studies, and IR-spectroscopic investigations. Gold-coated surfaces are well
suited for electrochemical studies, surface plasmon resonance (SPR) investigations, and studies
by quartz crystal microbalance (QCM). If the interaction between the solvent and the surface is
less favorable than that between the polymer and the surface, the polymer will adsorb from the
solution onto the substrate surface. Charged polystyrene sulfonate (PSS), which is soluble in
water, has the ability to adsorb onto various hydrophobic surfaces because of the equilibrium
adsorption, where the concentration of monomers of the polymer in the bulk solution is less than
their concentration close to the substrate surface(Klitzing et al., 1999). In the opposite case, when
the interaction between solvent and surface is more favorable than the interaction between
monomers of polymer and surface, the entropy of mixing will cause a depletion of
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