Speaker：Christopher Evans (University of Illinois, Urbana-Champaign)

Title: Leveraging dynamic covalent chemistry to control viscoelasticity and chemistry in polymer networks

Invited by Prof. Rongchun ZHANG

Time：July 14, 2022 (9:30 am)

Venue: Lecture Room 324, AISMST (Building #2, KeJiYuan, North Campus)

Online：Zoom 838 2582 9311

Faculties and students are warmly welcome.

Abstract:

Dynamic covalent bonds incorporated into a polymer network can lead to materials which are capable of being recycled, dissolved back to monomer, and self-heal in response to damage. Dynamic bonds can also dramatically impact the relaxation, viscoelasticity, and transport of small molecules through a polymer. I will first discuss 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. These model networks reveal the role of crosslink density and molecular scale chemistry effects on macroscopic relaxation and dissipation. Next, mixtures of dynamic bonds are incorporated into a single network to understand when multiple relaxation modes will be observed. Finally, I will discuss the role of network architectures and bond exchange on the transport of ions or small molecules through polymers. Dense networks restrict diffusion, while dynamic bonds provide a mechanism to enhance transport. Adding salt to dynamic networks affects not only the conductivity, but can also lead to coordination 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 the fundamental properties of polymers for a range of applications.

Brief Biography：

Chris Evans is an Assistant Professor in the Department of Materials Science and Engineering at the University of Illinois, Urbana-Champaign. He received his undergraduate degrees in Chemical Engineering and Chemistry at the University of Minnesota, and a Ph. D. in Chemical Engineering at Northwestern University followed by a postdoc position at both UC - Berkeley and UC - Santa Barbara. He is the recipient of an NSF CAREER, ACS Petroleum Research Fund New Investigator, and 3M Non-tenured Faculty awards. His research groups specialized in the physical chemistry of polymer networks with an emphasis on the role of dynamic covalent bonds and ionic interactions.