Mixed Conductive Soft Solids by Electrostatically Driven Network Formation of a Conjugated Polyelectrolyte

A conjugated polyelectrolyte (poly[2,6-(4,4-bis-potassium butanylsulfonate-4H-cydopenta-[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)], PCPDTBT-SO3K) assembles into a novel, hierarchical hydrogel structure with all structural evidence indicating dominant electrostatic rather than aromatic or mesogen interactions. PCPDTBT-SO3K forms an entangled polymer mesh, where polymer chains are tied together by ionic cross-links, comprising microgel clusters that percolate to form a macroscopic three-dimensional network. With increasing temperature, ions gain mobility to move toward the exterior of the microgel clusters, dissolving the ionic cross-links and inhibiting network percolation through electrostatic repulsion. While pi-pi stacking interactions may be present in a disorganized fashion, no long-range pi-pi stacking is evident in X-ray scattering. Soft materials based on PCPDTBT-SO3K remain semiconducting and exhibit elevated ionic conductivity at the structural reorganization temperature.