The second virial coefficient of polyelectrolytes

Abstract

The second virial coefficient of linear polyelectrolytes is extremely nonideal because of the electrostatic interaction between charges of ions as well as because of the polymeric character of polyions. In this paper, the second virial coefficients of sodium polystyrene-sulfonate of various molecular weights were determined by light-scattering technique in solutions of different ionic strengths. From the experimental results, the correction factors for the two kinds of nonideality were separately calculated. Then it was concluded that most of the nonideal behavior of linear polyelectrolytes arises from the strong electrostatic interaction between charges, but the contribution of the polymeric character of polyions also cannot be neglected. The correction factor for the nonideality due to the polymeric character of polyions was compared with the theories on the second virial coefficient of linear polymers. It was found that most theories, particularly the theory of Casassa and Markovitz and others, can explain the results well. The correction factor for the electrostatic interaction was also found to be as expected previously.