Polyelectrolytes are charged polymers, found widely in nature and in manufactured goods. Polyelectrolytes with opposite charges associate with each other, yielding versatile, soft solids suited for use as adhesives, medical dressings, membranes for purification, carriers for controlled drug release, and scaffolds for cell culture. These so-called "polyelectrolyte complexes" have also been discovered as membrane-less organelles within cells. Despite the promise and prevalence of polyelectrolyte complexes, it is not known why some combinations of polyelectrolytes make strong, rubbery materials while other combinations produce viscous fluids. This project will investigate broadly the fundamental relationships between the composition of individual polyelectrolytes and the properties of the hydrated complexes they form. This understanding will guide the design and application of known and new materials for new technologies. An emphasis on chemistry student education and training, including broadening participation in STEM, will expose participants to the latest ideas, techniques and problem-solving tools to better serve the flourishing polymers industry. Student participation in high-value video tutorials on aspects of polyelectrolytes will reach a broad audience of scientists and will help build professional presentation skills of young trainees involved.
A number of interesting and useful amorphous phases spontaneously assemble when polyelectrolytes of opposite charge, Pol+ and Pol-, are mixed. However, little is known concerning why different combinations of Pol+ and Pol- have substantially different association strengths. This work will quantitatively and systematically probe the dependence of Pol+/Pol- association on "hydrophobicity," or water content. Using robust synthetic methods, a series of increasingly hydrophobic cationic and anionic polymers will be prepared and complexed. The free energy of association will be determined by measuring, using sensitive radioisotope or spectroscopic methods, how easily Pol+Pol- ion pairs are broken by the addition of salt. At the same time, the amount of water in the complex will be determined with infrared spectroscopy. The results will correlate the strength of association to water content and number of methylene units added to enhance hydrophobicity. Complex formation between charged polypeptides will reveal the association strength of an ion pair or "salt bridge" formed between two amino acids. The fundamental insights resulting from the project will also impact the biological/health field since charged segment pairing of proteins is essential in protein folding (or misfolding). In a final thrust on polyelectrolyte interactions, the pairing strength between a polyelectrolyte and a nanoparticle of defined surface composition will be measured. The exceptional educational resources available at Florida State University's GEOSET studios will be employed to enhance the professional development of undergraduate and graduate students. Undergraduates, in particular women chemists, will be recruited through the University's undergrad research program and will be mentored in science and presentation skills. Building on previous successes within the research group, graduate students will collaborate to produce several informative, competitive, well-edited educational videos on polyelectrolytes and polyelectrolyte complexes.
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.
