Supramolecular Assemblies of a Semirigid Polyanion in Aqueous Solutions

In this article, we report the supramolecular assemblies of a semirigid polyelectrolyte, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT) in water. Cryo-TEM observation and SAXS measurement reveal that PBDT forms bundle-like structure even in very dilute concentration, C P, of 0.02 wt %. These bundle-like assemblies serve as new primary building blocks and self-assemble further as C P increases, to form large associations with or without long-range orientation. When 2 wt % < C P < 6 wt %, liquid–liquid phase separation occurs. Some of the supramolecular associations form bipolar liquid crystalline (LC) droplets via a typical nucleation and growth process. The droplets grow up by the coalescence of small ones and sediment under the gravity and coalesce to form a bottom nematic phase. When C P ≥ 6 wt %, the solutions are in a uniform nematic phase. The existence of these preliminary supramolecular assemblies of PBDT in aqueous solutions should be crucial for the formation of nematic LC phase at a significantly low C P, as well as the formation of macroscopic ordered structures in hydrogels via electrostatic interaction between PBDT and oppositely charge multivalent metallic ion or polycation.