Ionic Tunability of Conjugated Polyelectrolyte Solutions

Conjugated polyelectrolytes (CPEs), which combine a pi-conjugated polymer backbone with pendant ionic functionalities, offer an opportunity for electrostatic control of materials properties. In this work, the mesoscale morphology and physical properties of a high-mobility conjugated polyelectrolyte are tuned by the addition of salt, variation of the charge-compensating counterion, and complexation with an oppositely charged polyelectrolyte containing the same pi-conjugated back-bone. In systems with a single polyelectrolyte species, added ions screen the electrostatic repulsions stabilizing the gel-phase, resulting in the dissolution of ionic cross-links and hydrophobic collapse. Exchanging the charge compensating counterion is found to enable finer structural control of the solution behavior and modulation of the self-doping behavior. Finally, novel CPE-CPE complexes resulting in dense solutions and gels of semiconductive material are produced by combination of oppositely charged polyelectrolytes. Such concentrated CPE formulations should be useful materials for mixed electronic-ionic conduction and pseudocapacitative energy storage.