Temperature, water, and ion-pairing effects in polyelectrolyte complexes and multilayers*

It is largely accepted that the physical properties of polyelectrolyte complexes and multilayers are influenced by temperature, ionic strength, polyelectrolyte or salt type, pH, and water content, among other considerations. A growing body of knowledge points to the idea that many of these features ultimately control the number of polycation-polyanion “intrinsic” ion pairs and the lifetime of the intrinsic ion pair. This talk will discuss how the glass transition temperature and rheological properties relate to intrinsic ion pairing. Methods to quantify the number or fraction of intrinsic ion pairs in solid polyelectrolyte complexes and multilayers are discussed, along with a new method to estimate the number of water molecules at the intrinsic ion pair. Results suggest that the glass transition is related to the number of water molecules at the intrinsic ion pair. With regard to dynamic mechanical properties of solid complexes, time-temperature-water superpositioning is applied and a free-volume relationship is proposed. Results are complemented by all-atom molecular dynamics simulations.