Polyelectrolytes are water-soluble, charged polymers used in products ranging from shampoos to water purification treatments. If solutions of polyelectrolytes with opposite charges are mixed they precipitate into complexes that are biocompatible, rugged, elastic blends of the individual polymers. These complexes have potential medical applications in extended drug delivery and replacement for cartilage. They are also useful as membranes for water purification and desalination. Although their synthesis is straightforward, it has been impossible to process them into useful forms using heat softening, as is used for the more familiar "thermoplastics". This project will explore novel, versatile methods for softening and processing polyelectrolyte complexes using salt water instead of heat. Softening by adding salt, termed "saloplasticity", is a new technique that lowers energy consumption for polymer processing. Because it is performed with no volatile organic solvents it is also environmentally friendly. Several fundamental questions will be explored in this project: how do blends of different polymers respond to different salts? How is elasticity, essential for mimicking the properties of cartilage, controlled by salt? How can additional strength be built into saloplastics so they will last when used as replacements for intervertebral discs? At the same time these fundamental materials properties questions are explored, the project will support and promote international collaborations with the University of Strasbourg, France. Among the educational aspects of this project will also be a collaboration between the College of Business and the Department of Chemistry at Florida State University wherein Entrepreneurship and Chemistry students team up to write commercialization plans for technology developed by this and other projects.
Polyelectrolytes are water-soluble, charged polymers used in products ranging from shampoos to water purification treatments. If solutions of polyelectrolytes with opposite charges are mixed they precipitate into complexes that are biocompatible, rugged, viscoelastic blends of the individual polymers. Unlike traditional thermoplastics, polyelectrolyte complexes, PECs, cannot be processed when dry by heat softening. Instead, they may be plasticized with salt water. Increasing salt concentration progressively breaks the ionic pairing between polyelectrolytes. This "saloplasticity" is used along with heating to control the viscoelasticity of PECs. The overarching goal of this project is to probe the fundamental ways salt and heat are related to the properties of saloplastics. In the first of four subtopics, the glass transition, or softening temperature, of different pairs of polyelectrolytes with different strengths of interaction will be probed. The second part will look at the processing response of blends versus copolymers having the same composition. The next subtopic will attempt to answer fundamental questions about the role of molecular weight in saloplastic viscoelasticity. Finally, additional chemical crosslinks will be built into bulk saloplastics to stabilize the material for long-term use in biomedical applications such as artificial cartilage.
