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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 32: Poster Session II

CPP 32.8: Poster

Donnerstag, 20. März 2025, 09:30–12:00, P3

Is Anomalous Underscreening Detectable via AFM? — •Esther Ohnesorge, Thomas Tilger, Michalis Tsintsaris, and Regine von Klitzing — Department of Physics, Technische Universität Darmstadt, Darmstadt, 64289, Germany

Since colloidal dispersions have a significant importance in our daily life, it is of special interest to gain a deeper understanding of which interfacial forces govern their stability and how this stability can be tailored.

For aqueous electrolyte solutions, the DLVO theory is a powerful and well-established framework to describe these interactions at low and intermediate ionic strengths. In contrast, the situation at high ionic strength is less understood and the main methods for direct force measurements give inconsistent results. While the surface force apparatus (SFA) provides clear evidence for a reentrant behavior of the double layer repulsion in the highly concentrated regime - termed anomalous underscreening - for a wide range of different electrolytes, similar observations weren't possible with the atomic force microscope (AFM) to date. The reason for this fundamental difference is still unclear.

To elucidate the underlying mechanism, we performed colloidal probe AFM (CP-AFM) measurements in aqueous salt solutions. We systematically varied the type of salt, the surface chemistry of the confining surfaces (silica vs mica) as well as their curvature to bridge the gap between CP-AFM and SFA.

Keywords: Colloidal Probe AFM; Surface Forces; Electrolytes; Anomalous Underscreening