Block copolymers are a versatile materials platform for incorporating multiple functionalities into a single material by covalently tethering two or more homopolymers together. Due to the covalent attachment of the blocks, these materials self-assemble into morphologies with features on the 10s of nm length scale. We have investigated a series of BCPs based on an emerging class of ion-conducting polymers called polymerized ionic liquids (PILs) as well as a non-conductive structural block. PILs are polymers based on the familiar chemistries of ionic liquids but have either the cation or anion tethered to the polymer backbone. This minimizes leakage of the charged species into neighboring materials (for example in a thin film transistor) and also results in the current being carried by a single type of ion.
The role of nanoconfinement on the conductivity of imidazolium based PILs, where the imidazolium can act as a proton donor/acceptor and conduct protons, has been investigated. In polystyrene-PIL block copolymers, where the PIL is confined by a hard phase, an order of magnitude increase in the conductivity is observed in the block copolymer relative to the pure PIL. We attribute this to a change in the packing of the imidazolium PIL upon confinement which leads to more efficient pathways for proton transport through the phase separated domain. Substantial differences in the hydrogen bond network in the block copolymer are also observed via FTIR experiments. The effect of confinement is substantially reduced if a softer confining block, methyl acrylate, is employed. Finally, the conductivity in PS-PIL block copolymers is shown to scale with the domain size of the PIL.