Polyelectrolyte complex coacervation represents a unique form of liquid-liquid phase separation that has been hypothesized to resemble protocells, or prebiotic microcompartments that can localize biomacromolecules and direct chemical reactions. However, biological membraneless organelles materialize from not only charge-charge interactions, but also π/π stacking, hydrophobic effects, hydrogen bonding, patterned sequences, chirality, and other heterogenous non-covalent interactions in non-obvious ways. Engineering these attributes into bio-inspired charged polymers to modulate ion-pairing and control desired properties thus represents a major goal for the polyelectrolyte community in the next century of polymer science/engineering. To this end, we present recent efforts to deliberately incorporate these key features into bulk polyelectrolyte complexes. Oppositely charged styrenic homopolymers were controllably synthesized and paired together to investigate the structural evolution and changes in dynamics with added NaBr salt, which intuitively should transition in a continuum from solid precipitates to liquid coacervates to solution by breaking electrostatic associations. To our surprise, up to 2.5 M NaBr, the complex remained solid and stiffened; above this threshold to 4 M NaBr, frequency sweeps revealed a viscoelastic liquid response from the complex material. This phenomenon in dynamics was reproduced with parallel rheological studies with changing temperature, exhibiting consistent and reversible phase transition and relaxation dynamics. By combining thermogravimetric analysis, optical and cryo imaging, and small-angle X-ray scattering, we propose a mechanism to account for this unusual stimuli-responsive behavior and discuss how this can lead to new functional coacervate materials for a wide array of biomedical and industrial products.

Engineering molecular interactions beyond charge/charge interactions in functional polyelectrolyte complexes

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.