Mean activity coefficient for polyelectrolyte in mixed aqueous solutions of polyelectrolyte and simple electrolyte

The mean activity coefficient for polyelectrolyte in a mixed aqueous solution of polyelectrolyte and simple electrolyte is derived based on the condensation formalism previously reported [Biophys. Chem. 9, 397 (1979)]. Consistency is examined between the limiting laws, namely, for osmotic coefficient, for simple electrolyte activity coefficients, and for polyelectrolyte activity coefficient.