(3da) Understanding the Relationship Between Nanostructure and Ion Transport in Membranes for Energy Applications

Nanostructured membranes containing structural and ion-conducting domains are of great interest for a wide range of energy applications requiring high conductivity coupled with mechanical durability. Understanding the relationship between morphological and conductive properties of such materials is essential for designing optimal membranes. Here, I will discuss the relationship between nanostructure and ionic conductivity in mixtures of block copolymers with ionic liquids.  The mixtures self-assemble into well-defined nanostructures, where the ionic liquid selectively resides in one microphase. Scaling relationships have been developed to describe the conductivity of block copolymer/ionic liquid membranes as a function of block copolymer composition, ionic liquid concentration, and temperature. Furthermore, confinement to block copolymer nandomains is shown to affect the conductive properties of the ionic liquid. For instance, the hydrogen bond network in the proton-conducting ionic liquid imidazolium bis(trifluoromethylsulfonyl)imide ([Im][TFSI]) is altered by confinement to lamellar block copolymer nanodomains, leading to high levels of a fast proton “hopping” transport mechanism. As a result, the activation energy for ion transport is lower than in comparable membranes that do not self-assemble. These findings mark important progress in understanding how membrane composition, structure and ion transport are interrelated in nanostructured membranes, and lay the foundation for my future research plans.

Optimizing ion transport in nanostructured membranes is essential for devices relevant for energy generation and storage as well as for water purification and biological processes. My future research will focus on understanding mesostructure-property relationships that enable materials design for these applications. I will combine my expertise in block copolymer synthesis and morphological characterization with expertise in nuclear magnetic resonance (NMR) microscopy techniques, which have traditionally been used to characterize pore structure and molecular diffusion in porous media, and have the advantage of simultaneously probing structure and transport. This is a unique and powerful toolset for investigating structure-property relationships in nanostructured, ion-conducting systems.