Reduced viscosities of polyelectrolytes in the presence of added salts

Two different techniques for diluting polyelectrolyte solutions with salt solutions are discussed. The first is the so‐called isoionic dilution and the second is a method using salt solutions of concentrations so chosen as to make the reduced viscosity a linear function of polymer concentration. For isoionic dilutions, in which the total counterion concentration is kept constant, the reduced viscosity curves are not linear over the whole range but are rather sharply curved at the early stages of dilution. However, it is observed that the viscosity of solutions subject to such dilutions can be expressed by an empirical equation similar in form to that of Fuoss and Strauss. The second method is carried out by diluting the polymer solution with a simple salt solution whose concentration, c1, is selected by trial and error to make the reduced viscosity a linear function of concentration. The ratio r = c1/c0 where c0 is the concentration of counterions from the original polymer solution, increases as the charge density of the polyelectrolyte decreases and is rather insensitive to c0. The values of 1 − r obtained for the partially neutralized polyacrylate were compared with the degrees of counterion fixation obtained by electrolytic methods, and good agreement was found between the two.