Site-specific perspective on interactions in polyelectrolyte complexes: Toward quantitative understanding.

The composition and properties of hydrated polyelectrolyte complexes, PECs, depend strongly on the salt concentration of solutions in which they are immersed. This fascinating and polyelectrolyte-specific behavior is often treated with extensions of theory developed for single-component polyelectrolyte solutions. As an alternative, the response of PECs to salt (i.e., small ions) may be treated as a competition between the pairing of positive, Pol +, and negative, Pol -, repeat units and their salt counterions. Simple equilibrium expressions provide the degree of reversible Pol + Pol - pair breaking as more salt is added. This work summarizes the site-specific ion pairing view of PECs.