Christopher Evans, assistant professor of materials science and engineering, University of Illinois, Urbana-Champaign
"Impact of dynamic bonds on dissipation, crystallization, and ion transport in polymer networks"
Dynamic covalent bonds incorporated into a polymer network can lead to thermosets which capable of being recycled, dissolved back to monomer, and self-heal in response to damage. My research focuses on the role of dynamic bonds on relaxation, crystallization, and ion transport. In the first part of the talk, I will discuss silicone networks with fast exchanging bonds where the viscoelasticity is probed over a broad (200 K) temperature window and shows a breakdown of classical Arrhenius behavior expected in these networks. Under high-rate deformation imposed by shockwaves, these networks can dissipate substantially more energy than permanent networks and the dissipation scales with dynamic bond density. Next, semi-crystalline ethylene dynamic networks are investigated which exhibit very slow kinetics and distinct morphology relative to polyethylene, which is linked to dynamic bond exchange. In a third area, ethylene oxide networks are prepared with added salts to form self-healing electrolytes. The added salt affects the conductivity but can also coordinate with the dynamic bonds in the backbone giving rise to a rich interplay between the rheology and ion transport as a function of temperature. These studies point to the important roles of dynamic covalent chemistry on polymer physical properties for a range of applications.