Regensburg 2025 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 38: Interfaces and Thin Films II

CPP 38.4: Talk

Thursday, March 20, 2025, 17:15–17:30, H38

Anomalous Screening Behavior of Superchaotropic Ions — •Thomas Tilger, Esther Ohnesorge, Michalis Tsintsaris, and Regine von Klitzing — Department of Physics, Technische Universität Darmstadt, Darmstadt, 64289, Germany

Due to their special properties, which make them suitable for many applications such as wastewater treatment, separation of nuclear waste and the stabilization of foams, the interest in superchaotropic nano ions grew during the last years. Especially for the last application, it is crucial to understand how the presence of these ions modifies the interaction between interfaces.

To directly measure the forces between well-defined interfaces, colloidal probe atomic force microscopy (CP-AFM) has proven to be a powerful tool. As model system for nano ions we chose Keggin ions as well as dodecaborate clusters and investigated their influence on the interaction between colloidal silica beads in aqueous solutions.

It turned out that - despite the large ion size of up to one nanometer - the interaction between the silica beads can still be described by the classical DLVO-theory of electrolyte solutions, consisting of a van der Waals attraction and an electrostatic double layer repulsion. However, the obtained screening lengths exhibit a significant deviation from the ones expected according to the nominal ionic strength of the solutions. This might be a hint for an ion aggregation. The magnitude of the deviation depends on the type of nano ion as well as the concentration of the solution.

Keywords: Colloidal Probe AFM; Superchaotropes; Keggin Ions; Dodecaborates; Surface Forces