Counterion-Modulated Microphase Separation of a Solvent-Free Block Polyampholyte

Interfaces between oppositely charged polymers present strong local gradients in the electrical environment, enabling applications in electrochemical devices, ionic diodes, and low-voltage electroadhesives. As these responses are often highly dependent on the area of contact between the polymers, many efforts have been made to prepare structures with a high interfacial area to enhance performance. However, tailoring the miscibility of polycations and polyanions to realize targeted nanoscale structures remains an outstanding challenge. In this study, we present a novel approach to achieving microphase separation in solvent-free block polyampholytes by manipulating counterion chemistry. Using a block polyampholyte composed of a positively charged imidazolium block and a negatively charged sulfonylimide block, we demonstrate that the phase behavior can be modulated by the chemistry of the added ionic liquid salts. Specifically, immiscibility between a fixed alkyl-imidazolium and a bulky alkyl-phosphonium counterion drives microphase separation of the block polyampholyte. Theoretical predictions of microphase behavior support the experimental observation that the chemical incompatibility between like-charged species increases the propensity for microphase separation. This work highlights a facile route to realizing nanoscale structures of block polyampholytes using chemically incompatible ionic liquids.