(451d) Strong Electrostatics Decouple Block Copolymer Morphology from Composition

The intricate balance between polymer-polymer repulsions and chain composition defines the self-assembled nanoscale morphology in diblock copolymers (BCPs), enabling applications in patterning, membranes, 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) assemble over a wide compositional range into cylinders with the charged block forming the continuous matrix, and remarkably even when it is the minority component (e.g., 10%). Such observations, coupled with the considerably low dielectric constant of the charged block (2.2D), lead us to postulate that the CNBP composition is decoupled from its morphology in the strong electrostatic interaction limit. This conjecture is verified by detailed calculations, and quantitatively captured by the packing parameter used to understand surfactant self-assembly. This fundamental insight into CNBP self-assembly has attractive implications to ion transport.