Water, Salt, and Temperature Effects in Polyelectrolyte Complexes and Multilayers

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PART 1: NON-TECHNICAL SUMMARY This research concerns ultra-thin films of polymers containing electrical charges, which are known as "polyelectrolytes". They can be formed in multilayers and molecular complexes and are of interest in applications ranging from biomedical to temperature-responsive materials. Such polyelectrolytes undergo an unusual "glass-melt" or softening transition whose nature and time-dependence are not well understood. Here the PI proposes to evaluate the direct origin of this transition using experimental techniques that will probe it on a molecular level. This will provide a firm view of how the transition and its dynamics interrelate with regard to temperature, water, and charges arising from different salts. This project places a unique emphasis on salt type, where a broad range of salts with varying size, charge, and water interactions are examined. One possible outcome is a unified relationship among temperature, water, and salt as it governs the transition. This will be of significant importance because this new knowledge will allow fine-tuning of the transition temperature and the physical properties associated with these materials, ultimately leading to possible new advanced applications. A major element of the proposed research is to educate, mentor, and train a future generation of diverse workers skilled in science as well as to offer science outreach to the general public both locally and online. PART 2: TECHNICAL SUMMARY Experiments are proposed to investigate the nature of the thermal transition observed in hydrated polyelectrolyte complexes and multilayers. If successful, this project will shed new light on water's role in the thermal transition. Possible outcomes include the experimental verification of the role of polyanion-water interactions in the thermal transition, water and salt relationships with the thermal transition, and evidence of time-temperature-salt-water superpositioning. The proposed approach centers on quartz crystal microbalance with dissipation, differential scanning calorimetry, and electrochemical impedance spectroscopy, temperature-controlled Fourier transform infrared spectroscopy and dynamic mechanical analysis. The proposed project is comprised of four activities: (1) investigate water-poly(styrene sulfonate) interactions within polyelectrolyte multilayers as a function of temperature, (2) explore and determine the role of water and other solvents, (3) examine and understand the role of salt on the transition, and (4) determine possible water-salt connections and effects on dynamics associated with the transition. Educational components of the proposed work include training and mentoring of graduate and undergraduate students, as well as outreach locally and through the NAE EngineerGirl website.