PHASE-SEPARATION PHENOMENA AND VISCOSITY ENHANCEMENTS IN AQUEOUS MIXTURES OF POLY(STYRENESULFONATE) WITH POLY(ACRYLIC ACID) AT DIFFERENT DEGREES OF NEUTRALIZATION

Interactions between poly(styrenesulfonate) (PSS) and poly(acrylic aci d) (PA) in aqueous solution have been studied, with and without added salt, and at various degrees of neutralization (alpha) of PA. Equilibr ium phase diagrams have been determined, and the viscosities of monoph asic mixtures have been measured. Both types of experiments reveal str iking effects of alpha on the PA-PSS interactions. Salt-free mixtures with fully or partially neutralized poly(acrylic acid) phase separate segregatively, except at very low alpha where, instead, an association between PA and PSS occurs. The association is evidenced by a dramatic ally increased viscosity, relative to solutions of PA or PSS alone, in semidilute mixtures. Addition of salt (1 M NaCl) results in an increa sed two-phase area at all alpha, and in the appearance of an associati ve phase separation for non-neutralized PA. The qualitative phase beha vior observed in the presence of salt can be generated by calculations using the Flory-Huggins theory, if it is assumed that both the PSS-PA and the PA-solvent interactions change monotonically with alpha in a specified fashion. All experimental observations, and the theoretical modeling, suggest that the effective PA-PSS interaction changes (over a narrow interval of alpha) from an attraction at very low alpha to a repulsion at higher alpha.