Charge-driven co-assembly of polyelectrolytes across oil-water interfaces
Monteillet, H. ; Hagemans, F. ; Sprakel, J.H.B. - \ 2013
Soft Matter 9 (2013)47. - ISSN 1744-683X - p. 11270 - 11275.
controlled flocculation - opposite charge - small particles - emulsions - membranes
We report a simple strategy to co-assemble oppositely charged polyelectrolytes across oil–water interfaces; this allows the accumulation of an electrostatic complex at the interface of species that are not surface active by themselves. To this end, we use a new, oil-soluble anionic polymer, poly-(fluorene-co-benzothiadiazole-co-benzoic acid), in combination with a cationic polyelectrolyte that is dissolved in the aqueous phase. When only one of the two charged components is present, no positive adsorption is observed in interfacial tension measurements; by contrast, when both polyelectrolytes are present, in the oil and water phases respectively, a rapid decrease of the interfacial tension is observed, indicating co-adsorption of the cationic and anionic polyelectrolytes. The complexation strength can be tuned through changes in both ionic strength and pH. Confocal microscopy and co-localization analysis further verifies the presence of both polyelectrolytes at the interface. With this approach, emulsions can be stabilized for several weeks; moreover, using the sensitivity of the complex to changes in pH, we are able to reversibly break and make the emulsions on demand.
Reversible assembly of oppositely charged hairy colloids in water
Spruijt, E. ; Bakker, H.E. ; Kodger, T.E. ; Sprakel, J.H.B. ; Stuart, M.A.C. ; Gucht, J. van der - \ 2011
Soft Matter 7 (2011)18. - ISSN 1744-683X - p. 8281 - 8290.
transfer radical polymerization - diffusion-limited aggregation - dispersion polymerization - controlled flocculation - small particles - polar-solvents - janus spheres - gels - dna - heteroaggregation
We present an experimental study of the fully reversible assembly of oppositely charged colloidal particles in aqueous solutions. Our polystyrene colloids are charged by a grafted polyelectrolyte brush on their surface and stabilized at all salt concentrations by a neutral adsorbed polymer layer. Below a critical salt concentration oppositely charged colloids form clusters and gels with a fractal nature. The fractal dimension of those aggregates increases with increasing salt concentration. Above the critical salt concentration no aggregation takes place, due to the stabilizing neutral adsorbed polymer. Moreover, the aggregated structures are fully reversible and can be redispersed by simply increasing the salt concentration above the critical concentration. We confirm that time-dependent interaction forces are at the basis of the formation of clusters in the present system by atomic force microscopy measurements as a function of salt concentration and contact time. The force measurements show that the attraction between particles strengthens in time due to interpenetration of the polymer brushes, driven by polyelectrolyte complexation. These particles are a promising step toward a reversible and controlled self-assembling system in water, using colloidal particles as building blocks.