Counterions Control the Self-Assembly of Structurally Persistent Micelles: Theoretical Prediction and Experimental Observation of Stabilization by Sodium Ions

Authors

  • Christof M. Jäger M. Sc.,

    1. Computer-Chemie-Centrum and Interdisciplinary Center for Molecular Materials, Friedrich-Alexander Universität Erlangen-Nürnberg, Nägelsbachstr. 25, 91052 Erlangen (Germany), Fax: (+49) 9131-85-26565
    2. Excellence Cluster “Engineering of Advanced Materials”, Friedrich-Alexander Universität Erlangen-Nürnberg, Nägelsbachstr. 49b, 91052 Erlangen (Germany)
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  • Andreas Hirsch Prof. Dr.,

    1. Lehrstuhl für organische Chemie II and Interdisciplinary Center for Molecular Materials, Friedrich-Alexander Universität Erlangen-Nürnberg, Henkestr. 42, 91054 Erlangen (Germany)
    2. Excellence Cluster “Engineering of Advanced Materials”, Friedrich-Alexander Universität Erlangen-Nürnberg, Nägelsbachstr. 49b, 91052 Erlangen (Germany)
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  • Boris Schade Dr.,

    1. Forschungszentrum für Elektronenmikroskopie, Institut für Chemie und Biochemie, Freie Universität Berlin, Fabeckstraße 36a, 14195 Berlin (Germany)
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  • Christoph Böttcher Priv.-Doz.,

    1. Forschungszentrum für Elektronenmikroskopie, Institut für Chemie und Biochemie, Freie Universität Berlin, Fabeckstraße 36a, 14195 Berlin (Germany)
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  • Timothy Clark Prof. Dr.

    1. Computer-Chemie-Centrum and Interdisciplinary Center for Molecular Materials, Friedrich-Alexander Universität Erlangen-Nürnberg, Nägelsbachstr. 25, 91052 Erlangen (Germany), Fax: (+49) 9131-85-26565
    2. Excellence Cluster “Engineering of Advanced Materials”, Friedrich-Alexander Universität Erlangen-Nürnberg, Nägelsbachstr. 49b, 91052 Erlangen (Germany)
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Abstract

We show by molecular-dynamics (MD) simulations and cryo-transmission electron microscopy (cryo-TEM) experiments that the size and form of structurally persistent micelles formed by the T-shaped amphiphile 1 are controlled by the counterions. The two techniques reveal that the micelles are specifically stabilized by sodium counterions relative to potassium ions. Both the simulations and the cryo-TEM experiments suggest that the micelles are stabilized by strongly conserved hydrated contact ion pairs with sodium counterions but not with potassium ions. We suggest that the TEM is observing local high density due to hydrated carboxylate/sodium ion pairs at the surface of the micelle. A high concentration of such structures is found in MD simulations with sodium counterions, but not with potassium.

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