Adsorption of polyelectrolytes onto the oppositely charged surface of tubular J-aggregates of a cyanine dye
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The adsorption of three different polycations at the negatively charged surface of tubular J-aggregates of the amphiphilic cyanine dye 3,3′-bis(2-sulfopropyl)-5,5′,6,6′-tetrachloro-1,1′-dioctylbenzimidacarbocyanine (C8S3) is investigated by means of cryogenic electron microscopy and optical absorption spectroscopy. All three polycations could be adsorbed at the tubular aggregates without flocculation or precipitation when added in molar amounts of monomers sufficiently smaller than that of the dye molecules. It is found that preferably, a minority of aggregates is coated by the polycations while a majority of aggregates is left uncoated. For the coated aggregates, the adsorption leads to charge reversal of the aggregate surface as supported by zeta potential measurements. The morphology of the coating differs significantly for the three polycations: The branched polycation polyethylenimine (PEI) attaches to the tubular aggregate by hit-and-stick adsorption of the coiled state in solution forming irregular clot-like coatings; the flexible and weakly cationic poly (allylamine hydrochloride) (PAH) forms a more homogeneous coating but destroys the integrity of the dye aggregate; the more hydrophobic and strong polycation poly (diallyldimethylammonium chloride) (PDADMAC) forms a thin and homogeneous layer, supposedly by wrapping around the tubular aggregate. For the latter growth of a second double layer of dyes is observed for the aggregates. The different morphologies of the coating layers are explained by the details of the chemical structure of the polycations. The possible adsorption of polyelectrolytes at these amphiphilic tubular structures, stabilized by means of hydrophobic forces, is far from obvious and demonstrates an applicable route to the build-up of more complex nanostructures in solution by means of a self-assembly process.
KeywordsPolyelectrolyte J-aggregate Tubular aggregate Layer-by-layer adsorption
This work was supported by Deutsche Forschungsgemeinschaft (DFG) via the Max-Planck Research School on Biomimetic Systems, the Collaborative Research Centre 951 (“Hybrid Inorganic/Organic Systems for Opto-Electronics (HIOS)”), and the Collaborative Research Centre 448 (“Mesoscopically structured systems”). We gratefully acknowledge the Joint Lab of Structural Research between Helmholtz-Zentrum Berlin, Humboldt-Universität zu Berlin and Technische Universität Berlin. We thank Yan Qiao for support and valuable discussions and we are grateful to E. Poblenz for her help with sample preparation.
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Conflict of interest
The authors declare that they have no conflict of interest.
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