Colloidal properties and gelation of aqueous dispersions of conductive poly(benzimidazobenzophenanthroline) derivatives
2013
Hirvonen, Sami-Pekka | Karesoja, Mikko | Karjalainen, Erno | Hietala, Sami | Laurinmäki, Pasi | Vesanen, Eevakaisa | Butcher, Sarah J. | Tenhu, Heikki
Poly(benzimidazobenzophenanthroline), BBL, is a practically insoluble conductive polymer. It can be gradually dispersed in water, however by dialysis and sonication, i.e. during the purification and dilution right after synthesis. Dispersions with higher solids content and colloidal stability were prepared 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 negatively-charged particles with a broad size distribution. These dispersions were found to be sensitive to ionic strength. Salting out occurred within a NaCl concentration range of 0.5–4 mM and some samples showed re-entrant behavior with redispersion upon further salt addition. Addition of a non-ionic surfactant was found to enhance the stability of BBL–PEO dispersions against salting-out. Upon increasing the polymer concentration the dispersions form gels upon resting. The strength of the gels depends on the total polymer concentration 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.
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