(32b) Charge-Based Control of Polyelectrolyte Block Copolymers
Polymer electrolytes based on block copolymers are a promising contender for ion transport in batteries, due to their safety compared to liquid electrolytes. However, challenges remain in designing these materials; block copolymers are sought after due to the ability to combine the mechanical stability of a glassy block with the ion transport properties of an ion-transporting block (typically poly(ethylene oxide), PEO). Upon adding a salt to mediate ion transport, this system is effectively rendered a block copolyelectrolyte with a “charged” PEO block that drastically alters the block copolymer morphology. The resulting physical system is difficult to understand due to the many levels of length scale inherent to these problems - both charge length scale as well as polymer morphology length scales are important. We have developed a theoretical method to calculate the effect of charge thermodynamics on polymer morphology, and can demonstrate how the introduction of charge along a polymer backbone can in fact be used to govern the behavior of block copolymers in a predictable and controllable fashion. Concepts such as charge size, charge cohesion, and ion entropy reveal a rich parameter space in which it is possible to use charge to tune through an array of polymer morphologies. Physical intuition elucidated by this study will hopefully guide the targeted design of new polymer-based battery electrolyte materials and more generally motivate the use of charge as a tool to govern the structure of block copolymer materials.