a) b - École Polytechnique de Montréal

Figure 2-39. Macromolecule with a) small persistence length, b) medium persistence length,
and c) large persistence length
In the adsorption of a single polyelectrolyte chain on the surface, confinement in the adsorbed
layer causes an entropic repulsion. If the effective persistence length of the polymer is much
larger than the thickness of the adsorbed layer, an extended chain on the surface is observed
(Figure 2-40a). In contrast, a random coil with many loops within the adsorbed layer is generated
if the effective persistence length is smaller than layer thickness.
Figure 2-40. Schematic picture of a) the adsorbed
polymer layer when the effective persistence length is
large, (b) Adsorbed layer for the case when the
persistence length is small. In this case the polymer
forms a random coil with many loops
a)
c)
Consequently, electrostatic interactions play a major role in the adsorption of polyelectrolytes.
Other important parameters affecting electrostatic interactions, besides the charged monomers,
are the surface charge density, or surface potential in the case of conducting surfaces, the
concentration of salt in the solution, or ionic strength of low molecular weight electrolyte, and
the pH of the solution.
a)
b)
b)
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