Thermodynamics and Design of Sequence-Defined Polyelectrolyte Complexes

Charged polymers known as polyelectrolytes have been studied for decades, however understanding their physical properties remains a persistent challenge for polymer scientists. This difficulty stems from the intricate interplay between length scales spanning as much as 3-4 orders of magnitude, which has stymied our understanding of a truly important class of polymers; polyelectrolytes are widely used in applications ranging from food additives to paints, and most biopolymers (proteins, DNA, polysaccharides) are also polyelectrolytes.

However, the complexity of charged polymers can be harnessed for molecular-level materials design. Inspired by sequence-specific behaviors in biomolecular condensates, intracellular structures that assemble in part by electrostatic interactions, we study phase separation phenomena in sequence-defined polyelectrolytes. We are specifically interested in a class of polyelectrolyte materials known as complex coacervates, which are aqueous solutions of oppositely-charged polyelectrolytes and salt that can exhibit associative phase separation. We pursue an integrated experimental, computational, and theoretical study to demonstrate that coacervates are highly sensitive to the precise patterning of charges, as well as the chemistry of the polymer itself. We elucidate the key molecular features that play a large role in coacervate thermodynamics. Building upon these insights, we demonstrate how coacervate phase behavior can be strongly tuned via specific charge sequences, how the distribution of charge can be used to facilitate the selective uptake of proteins, and how phase behavior affects coacervate rheology and processing. Ultimately, our goal is to establish molecular-level design rules to facilitate the tailored creation of materials based on complex coacervation that can both illuminate self-assembly phenomena found in nature, and find utility across a wide range of real-world applications.