Self-Assembling Structure in Solution of a Semirigid Polyelectrolyte

We investigated the self-assembling structure in aqueous solution of polyelectrolyte poly(2,2‘-disulfonyl-4,4‘-benzidine terephthalamide) (PBDT), which has a rigid chemical structure of polyaramide in the main chain. It is found that PBDT exhibits a stretched semirigid conformation in solution, regardless of PBDT concentration, C P, or salt addition. PBDT in water exhibits both a very low overlap concentration, C *, and a lower critical concentration of nematic liquid crystal, C LC *. In the intermediate region of C * < C P < C LC *, PBDT forms cluster-like isotropic self-assembly. Moreover, in the intermediate region of C * < C P < C LC *, the addition of NaCl induces the alternation of structure from a cluster-like isotropic self-assembly to a fiber-like anisotropic one. Further addition of NaCl induces a network-like huge self-assembling structure, as the stoichiometric molar ratio of [NaCl] to [NaSO 3 - ] increases beyond 1. The semirigid polyelectrolyte probably has hidden potential for structural polymorphism in aqueous solutions in the presence of salt.