Conformations similar to ‘‘pancakes’’ and ‘‘brushes’’ can also occur for
adsorbed polymers. To achieve substantial repulsive action, a brush is
generally desired; to that end, a good solvent quality and a high number
density are needed.
A polymer layer, whether adsorbed or grafted, can cause so-called
steric repulsion. Two mechanisms can be distinguished, as illustrated in
Figure 12.6. If the proximity of a second particlerestricts the volumein
which the protruding polymer chains can be, this means that the number of
conformations that a chain can assume is restricted, hence the entropy of
these chains is lowered, hence the free energy is increased, hence a repulsive
FIGURE12.6 Two mechanisms involved in steric repulsion due to grafted (or
adsorbed) polymer chains (heavy lines). The dotted lines indicate possible
conformations of the polymer chain in the absence of volume restriction.