Imidazolium sulfonate-containing pentablock copolymer–ionic liquid membranes for electroactive actuators†

Electromechanical polymeric transducers have received significant attention recently for many emerging applications, including electromechanical actuators, sensors, electro-active coatings, and artificial muscles. Desirable physical properties for polymeric membranes in electromechanical transducers include high ionic conductivity, tunable modulus versus temperature behavior, efficient response at relatively low voltages (<5 V), and facile fabrication processes. However, only a few families of polymeric materials fully satisfy these requirements, and in most instances, anionic ionomers with random placement of sulfonates and carboxylates are leading candidates. Moreover, sulfonic acid containing polymers suffer from poor thermal stability due to low temperature degradation reactions. There remains a unique opportunity for the design of multiphase block copolymers wherein the nanoscale morphology presents (1) an imidazolium sulfonate, polar phase for ion-conductivity in the presence of added electrolyte, and (2) a nonpolar phase that imparts acceptable thermomechanical performance. Block copolymer–ionic liquid composite membranes have emerged as promising candidates for electromechanical transducer applications. Due to microphase separation of different immiscible sequences, block copolymers self-assemble into nanostructured materials and exhibit a combination of multiple properties. Tailoring sequence length, molecular weight distribution, and chemical composition of each block generates various nanostructured materials for applications in water purification, fuel cell membranes, energy harvesting, and energy storage. Spontak et al. recently described the fabrication of electroactive membranes using non-neutralized sulfonic acid-containing pentablock copolymers swollen with high levels of ethylene glycol and glycerol