Ion Transport in Well-Aligned Block Copolymer Electrolytes

The independently tunable electrical and mechanical properties of block copolymer electrolytes (BCPEs) makes them attractive candidates for ion exchange membranes. However, these materials often show a lower conductivity even after accounting for the reduced volume fraction of the conducting phase. This reduction in conductivity has been ascribed to the tortuosity of the conducting pathways, poorly connected domains, grain boundaries, and low mobility near the BCP interface. It is often difficult to differentiate these nanoscale hinderances to transport in microns-thick membranes due to the inability to fully control the orientation of the BCP domains. Here, we present a new approach to this problem wherein we can fully align the conductive domains of a BCPE along the direction of the electric field produced by interdigitated electrodes (IDEs), thus enabling us to divorce morphological from molecular-level effects. We observe that a low mobility region near the block copolymer interface might explain the lower conductivity of BCPEs compared to an equivalent volume fraction of homopolymer electrolyte.