SPECIFIC COUNTERION BINDING TO CATIONIC POLYELECTROLYTES

Following D. J. Flory the authors define a theta solvent for a polymer as one in which the molecules are unperturbed and the second virial coefficient is zero. The solvent quality of water for a cationic polyelectrolyte can be altered by the addition of simple inorganic salts. Increased salt concentration provides increased charge shielding by the counterion until the molecules reach an unperturbed state. The solvent has become a theta solvent, and the salt concentration at this point may be conveniently called the theta salt concentration. In this paper the authors show that the concentration of an inorganic salt needed to produce theta conditions for a cationic polyelectrolyte varies widely, and depends primarily upon the polarizability of the anion.