Consistent with our previous notation, this equation constitute the Flory-Huggins entropy of mixing of all the species, 68 including the polycation (P +), polyanion (P -), cation (+), anion (-), and water solvent (W ), with the parenthesis indicating the corresponding subscript. The values φ α and N α are the volume fraction and molecular weight respectively of component α, assuming a reference volume ν 0 that is the molar volume of the salt, monomer, and water species. We note that the current formalism does not lead to the usual mixing entropy constraint that i φ i = 1, which in the real system would emerge from the inclusion of e.g. the hard-core repulsions associated with the solvent. In this implicit solvent model, we simply add this constraint ad-hoc and note that the pairwise potentials used in this work are actually potentials of mean force resulting from integrating out the solvent degrees of freedom.