Cluster Theory of Polyelectrolyte Solutions. II. Additivity Rules, Osmotic Pressure, and Donnan Equilibrium

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Abstract
We apply the results of the previous paper describing the free energy of a polyelectrolyte-added salt solution to the derivation of a relation between the osmotic coefficient and the activity coefficients of the mobile ions. From this relation, observed to be in excellent agreement with experiment, we obtain expressions resembling the empirical additivity rules. We conclude that the concept of ion binding may not be the appropriate way to interpret these rules. We also obtain an expression for the Donnan distribution of mobile ions and discuss the difficulties involved in the calculation of the Donnan osmotic pressure.