Tailoring Transport Pathways in Lamellar-forming Ionic Block Copolymers

Block copolymers (BCPs) composed of neutral and ionic liquid blocks are considered promising materials for energy storage and conversion applications. However, prior studies have found that the bulk ionic conductivity of certain BCPs with a lamellar structure is lower than what would be inferred based on the composition and the ionic conductivity of the corresponding polymeric ionic liquid (PIL) homopolymer. This effect has been partly attributed to insufficient connectivity among the lamellae ionic domains. In addition, it has been hypothesized that introducing ”conductive defects” into the lamellar structure should significantly enhance the bulk ionic conductivity. To test this point, we have studied the ionic conductivity of a series of high-molecular-weight lamellar block copolymers. The ordering kinetics are suppressed in these samples, leading to poorly ordered lamellae, and the bulk ionic conductivity is therefore elevated toward the expected value. When the effect of glass transition temperature is further considered, some BCPs perform better than expected.