(352a) Stimuli-Responsive Phase Behavior in Poly(diallydimethylammonium)–Poly(acrylic acid) Complexes: Effects of Mixing Ratio, pH and Temperature

The stimuli responsiveness of charge-driven assemblies forms the foundation for functional materials in water purification, biotechnology, and medicine. The self-assembly of oppositely charged polyelectrolytes is governed by several factors, including ionic strength, mixing ratio, and pH - specifically, in polyelectrolyte systems, where ionizability and hydrogen bonding play critical roles in polymer-solvent interactions and upper critical solution temperature (UCST) behaviors.

In this work, we investigate the solid-liquid-solution phase separation behavior of poly(diallyldimethylammonium)-poly(acrylic acid) (PDADMA-PAA) complexes by systematically tuning ionizability (via pH), PDADMA mixing ratios, KBr ionic strength, and temperature. UV-Vis spectroscopy and optical microscopy were used to establish a phase map of the solid-liquid-solution regimes. Thermal transitions were then examined up to 75 ⷪC to identify the UCST behavior. Thermogravimetric analysis (TGA) provided polymer, salt, and water content for constructing binodal phase diagrams at pH 5 and 6.

Our findings reveal distinct pH-dependent phase separation, with re-entrant phase behavior observed at pH 5. These results offer insights into the interplay of hydrogen bonding and electrostatics in complex coacervates and highlight strategies for tuning next-generation stimuli-responsive soft materials.