Events

Dynamic covalent bonds in polymer networks have shown great promise for imparting recyclability and self-healing into otherwise intractable materials. Recently, our group has leveraged bond exchange as means to control the complex viscoelasticity of polymer networks as well as mass and ion transport. For a fixed polymer chemistry, networks with dynamic bonds spanning five orders of magnitude in exchange rates have been investigated showing how modulus and network relaxation time are independently tunable. In the case of the fastest exchanging bonds, high crosslink density networks were prepared with small mesh sizes to investigate molecular probe diffusion where the penetrant approaches the mesh size. Remarkably, orders of magnitude enhancements in penetrant diffusion are observed in networks with fast bond exchange relative to analogs with much slower or permanent crosslinks. This effect grows with increasing crosslink density, and persists even in networks approaching their glassy state. Dynamic networks were also investigated with added salt which can coordinate to various bond chemistries. Salt can either increase or decrease modulus, while invariably accelerating bond exchange leading to faster bulk relaxation times. The impact of salt-dynamic bond interactions on conductivity will also be discussed in the context of added Li salts. In summary, our work points to the key role dynamic covalent chemistry can play in designing materials for mass and ion transport, including membranes for selective separations and electrolytes.

Prof. Evans is an Associate Professor in Materials Science and Engineering at the University of Illinois, Urbana-Champaign. His group focuses on the chemistry and physics of dynamic polymer networks, as well as mass and ion transport in a range of polymeric systems. He is the recipient of an NSF CAREER award, ACS PRF New Investigator award, PMSE Young Investigator award, and 3M Non-tenured Faculty award.