What conjugated polyelectrolytes tell us about aggregation in polyelectrolyte/surfactant systems

The interaction between conjugated polyelectrolytes (CPEs) and surfactants in aqueous solutions is reviewed, based on results from absorption and fluorescence spectroscopy, NMR, dynamic light scattering (DLS), small angle X-ray (SAXS) and neutron (SANS) scattering, electrical conductivity and molecular dynamics simulations. It is shown that the conjugated polyelectrolytes frequently form aggregates (clusters) in water, but these can be broken up by the addition of co-solvents or surfactants. With oppositely charged surfactants, both enhancement and quenching of fluorescence are observed, depending on the nature of the CPE. These interactions start at very low surfactant concentrations, and, in some cases, associative phase separation is observed. However, there is little evidence for the pearl necklace structures observed with surfactants and nonconjugated polyelectrolytes. This may be related to the greater chain rigidity of the CPEs. Associative interactions are also seen with CPEs and non-ionic surfactants, which efficiently break-up the CPE aggregates to form mixed systems with greatly enhanced fluorescence. The relevance of these results to both the nanostructuring of conjugated polyelectrolytes and to our general understanding of polyelectrolyte-surfactant systems will be discussed. (C) 2015 Elsevier B.V. All rights reserved.