CPOS Seminar: "The Role of Charge-based Interactions on Water and Polymer Dynamics"

Speaker: Harrison Landfield, Postdoctoral Researcher / Segalman and Shell Groups / Department of Chemical Engineering / UCSB

Charge-containing macromolecules are vital to applications in Biology, Electronics, Coatings, and Separations where the balance of important non-electrostatic and charge-based interactions combine to govern system behavior. The nature of these interactions is highly dependent on the local environment surrounding the macromolecules. Here, we will discuss the role of polymer concentration, charge proximity, and solvation environment on system dynamics. The first part of the talk will focus on the use of fluorescence-based single particle tracking studies to observe polymer self-diffusion through concentrated, charge-laden environments. This study reveals an extreme concentration dependence for polymer dynamics in highly crowded environments across a series of pH and counterion conditions and that cannot be predicted using traditional single-chain theories. These hindered system dynamics appear universal to polyelectrolyte systems and are attributed to the large effective excluded volumes of polyelectrolyte chains inducing glassy dynamics. Observations from these systems are applicable to crowded biological systems, such as intracellular environments where protein mobility is strongly inhibited and biomolecular condensates. The second part of the talk will discuss the use of highly localized Overhauser Dynamic Nuclear Polarization (ODNP) NMR to understand solvation dynamics within 15 Å of macromolecular surfaces. Studies of hydration dynamics around superabsorbent poly(acrylic acid) chains reveal non-monotonic trends with respect to polymer concentration and highlight the importance of pH on polymer conformations and system dynamics. Additionally, this experimental approach is used to gauge hydration dynamics within ion separation membranes to understand the role of charge-based modifications on system dynamics. These studies highlight the need for highly localized measurements, as macroscopic dynamics trends vary greatly from the localized trends observed. Overall, these studies highlight the role of short-range, localized interactions on macromolecular solution behavior and represent an opportunity to further refine these systems.