Ionic Tunability of Conjugated Polyelectrolyte Solutions

Abstract

Conjugated polyelectrolytes (CPEs), which combine a π-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 π-conjugated backbone. 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.