Berlin 2024 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 15: Poster I

CPP 15.19: Poster

Monday, March 18, 2024, 18:00–20:00, Poster C

Electrostatic Screening in Highly Concentrated Salt Solutions — •Esther Ohnesorge, Thomas Tilger, 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 get 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 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 different types of salt solutions, close to their solubility limit. As confining surfaces, silica and mica were compared to study the influence of the surface charge density and to bridge the gap between CP-AFM and SFA.

Keywords: Colloidal Probe AFM; Surface Forces; DLVO Theory; Electrolytes; Underscreening