Colloidal properties and gelation of aqueous dispersions of conductive poly(benzimidazobenzophenanthroline) derivatives

Poly(benzimidazobenzophenanthroline), BBL, is a practically insol. conductive polymer. It can be gradually dispersed in water, however by dialysis and sonication, i.e. during the purifn. and diln. right after synthesis. Dispersions with higher solids content and colloidal stability were prepd. by first turning the polymer amphiphilic adding poly(ethylene oxide), PEO, into BBL chain ends (BBL-PEO). Dynamic light scattering and zeta potential measurements showed that the dispersions consist of neg.-charged particles with a broad size distribution. These dispersions were found to be sensitive to ionic strength. Salting out occurred within a NaCl concn. range of 0.5-4 mM and some samples showed re-entrant behavior with redispersion upon further salt addn. Addn. of a non-ionic surfactant was found to enhance the stability of BBL-PEO dispersions against salting-out. Upon increasing the polymer concn. the dispersions form gels upon resting. The strength of the gels depends on the total polymer concn. as well as the proportions of BBL and PEO in the BBL-PEOs. The gel formation was attributed to a formation of a network of nano-wire-type aggregates, which was verified with electron cryo-microscopy. [on SciFinder(R)]