CAREER: Using electrostatic interactions to guide microstructure and mechanical properties in block polyelectrolytes

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NON-TECHNICAL SUMMARY: Polyelectrolytes are polymeric materials containing electrically charged chemical groups and have been implemented in a number of important technologies. These include separations membranes (e.g., gas or water purification), energy storage and harvesting devices (e.g., Li-ion batteries, ion exchange membranes, or organic photovoltaics), and materials for biomedical applications. The polymers utilized in these applications require organization and assembly at the nanometer scale, which is often difficult to predict and control in polyelectrolyte systems. This limitation often stems from difficulties related to controlling polyelectrolyte synthesis as well as inconsistencies in polymer characteristics that appear in the literature. As a consequence, surveying the literature precludes an empirical prediction of polyelectrolyte behavior. This CAREER project will utilize a modular synthetic strategy to reproducibly control the amount and type of charged groups within the polyelectrolyte, thus enabling correlations between polymer characteristics and application-specific criteria, such as nanoscale assembly features and mechanical properties. Additionally, educational materials related to polymer science will be delivered to local K-12 teachers, who will also be trained in integrating problem-based learning into their curricula. Furthermore, this project will engage undergraduate and graduate students, and highlight the importance and impact of polymer science to the surrounding public community.TECHNICAL SUMMARY:Establishing empirical structure-property design rules for polyelectrolytes through a survey of the literature is impractical due to the variations in synthetic platforms, molecular weight distributions, and absolute molecular weights reported. Recent theoretical work has identified ion entropy, ion solubility, and molecular-range electrostatic interactions as key parameters that synergistically influence the morphology of block polyelectrolytes. Therefore, this project will employ living anionic polymerization to prepare a diblock tetrapolymer (i.e., two blocks, four monomers) precursor with tunable molecular weight and narrow molecular weight distributions. Subsequently, the precursor will undergo orthogonal post-polymerization functionalization to controllably introduce various charge types (e.g., combinations of sulfonate, ammonium, and triazolium ions) at various charge densities. This approach enables experimental correlation of charge type, charge density, and backbone composition to ion solvation, counterion entropy, and electrostatic cohesion and ultimately to microphase separation and rheological properties. Thus, the outcome of this work will demonstrate strategies, in the form of empirical design rules that complement recent theoretical outcomes, to design application-specific performance based on counterion entropy, ion solvation, and long-range Coulombic interactions in polyelectrolyte materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.