Compositionally Asymmetric Block Polyelectrolyte Morphologies*

The delicate balance of (short ranged) enthalpic interactions and entropic factors direct the self-assembly in nonionic diblock copolymers (BCPs) which is exploited in a broad range of applications, e.g., lithography, energy storage, membrane separations, and optics. We demonstrate that such behavior is profoundly altered when one block carries a charged trisaminocyclopropenium (TAC) ion at each monomer. These charged-neutral copolymers (CNBPs) display strongly asymmetric morphology maps with the unique aspect that the minority component, the charged block, has a strong propensity to form the continuous matrix. Such observations, coupled with the unexpectedly low TAC dielectric constant (~2.5) lead us to postulate that the CNBP morphology is strongly modified by long-range electrostatics. This conjecture is verified by detailed geometric calculations and quantitatively captured by a simplistic scaling model derived from surfactant self-assembly principles. This fundamental insight into the role of strong electrostatics on CNBP self-assembly has attractive implications for ion transport in polymeric media while simultaneously improving their mechanical properties.