Preparation of Poly(acrylate)/Poly(diallyldimethylammonium) Coacervates without Small Counterions and Their Phase Behavior upon Salt Addition towards Poly-Ions Segregation.

In this work, we report the phase behavior of polyelectrolyte complex coacervates (PECs) of poly(acrylate) (PA-) and poly(diallyldimethylammonium) (PDADMA+) in the presence of inorganic salts. Titrations of the polyelectrolytes in their acidic and alkaline forms were performed to obtain the coacervates in the absence of their small counterions. This approach was previously applied to the preparation of polymer-surfactant complexes, and we demonstrate that it also succeeded in producing complexes free of small counterions with a low extent of Hofmann elimination. For phase behavior studies, two different molar masses of poly(acrylate) and two different salts were employed over a wide concentration range. It was possible to define the regions at which associative and segregative phase separation take place. The latter one was exploited in more details because the segregation phenomenon in mixtures of oppositely charged polyelectrolytes is scarcely reported. Phase composition analyses showed that there is a strong segregation for both PA- and PDADMA+, who are accompanied by their small counterions. These results demonstrate that the occurrence of poly-ion segregation in these mixtures depends on the anion involved: in this case, it was observed with NaCl, but not with Na2SO4.

From Associative to Segregative Phase Separation: The Phase Behavior of Poly(acrylate)/Dodecyltrimethylammonium Complex Salts in the Presence of NaBr and NaCl.

We report here a systematic study on the phase behavior of dodecyltrimethylammonium-poly(acrylate) (C12TAPA) complex salts upon addition of simple salts (NaBr and NaCl). Complex salts of poly(acrylate) of two molar masses were employed (2000 and 450,000 g mol-1). Systems containing different surfactant mesophases were observed, whose structures were elucidated by small-angle X-ray scattering analyses. Overall, we observe a transition from associative to segregative phase separation intercalated with monophasic regions. In terms of surfactant association, a transition from micellar cubic phases to an isotropic micellar solution was observed, where these two phases occur in equilibrium with a dilute phase as a consequence of associative phase separation. However, as the salt concentration increases, segregative phase separation is observed, and scattering analyses of the surfactant-rich phase indicate the growth of micellar aggregates. These results are discussed in terms of the electrolyte effect screening the interactions between the oppositely charged surfactant and polymer and as a result of salting-out effects of the different electrolytes that prevail at higher concentrations.