PHASE-STABILITY OF POLYELECTROLYTE SOLUTIONS AS PREDICTED FROM LATTICE MEAN-FIELD THEORY

An extension of the Flory-Huggins lattice theory to include charged po lymers is described and utilized to predict the polymer solubility in solvent/polymer and solvent/polymer/salt systems and the polymer misci bility in solvent/polymer 1/polymer 2 systems. In the extended theory, all simple ions (counterions to the polymer and ions from the salt) ar e treated on the same level as the other components and the effect of the electrostatic interaction is included by imposing electroneutral p hases. It was found that charging the polymer generally increases the polymer solvency or polymer miscibility. In those cases where both pol ymers carry charges of the same sign, the minimal miscibility is obtai ned at such conditions that the coexisting phases have similar counter ion concentration. Generally, the increased solubility/miscibility cou ld be attributed to the contribution from the mixing entropy of the sm all ions. Good qualitative agreement with several experimental investi gations are found. The increased solubility of alkoxy polymers in aque ous solution upon an introduction of charged groups is also investigat ed.