Electrostatics in Macromolecular Solutions - Food Colloids: Self-Assembly and Material Science - page 147

Figure 12 Free energy of interaction between two charged spheres as a function of separa-
tion. (a) Situations in the presence of a polyelectrolyte salt (solid line) and in the
presence of a 1:1 salt (dashed line). The charge of the aggregates is 10e and the
radius is 10 A ˚ . The freely jointed polyelectrolyte chain contains 10 charged
monomers separated by a distance of 6 A ˚ . (b) Two negatively charged spheres in
the presence of a single neutral polyampholyte chain with 40 monomers.
The charge topology has been varied and the following notation is used: diblock
(solid line with no symbols), triblock (+10, 20,+10) (circles), tetrablock
(+10, 10,+10, 10) (squares) and 'reversed' triblock ( 10,+20, 10)
(diamonds). Each macromolecule has a charge of +20e and the radius is 10 A ˚
A polyelectrolyte adsorbs readily to an oppositely charged macromolecule,
and in the presence of several charged spheres it is, of course, entropically
favourable for the chain to adsorb to more than one sphere. This can only be
accomplished at short separations, since the chain tries to avoid placing charges
far from the charged aggregates, where the potential is high. Thus, a weakly