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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 18: Complex Fluids and Colloids, Micelles and Vesicles (joint session CPP/DY)

CPP 18.2: Vortrag

Dienstag, 6. September 2022, 12:00–12:15, H38

Electrostatic Shielding Behavior of Keggin Anions in Aqueous Solution — •Thomas Tilger and Regine von Klitzing — Department of Physics, Technische Universität Darmstadt, Darmstadt, 64289, Germany

Natural colloidal dispersions have accompanied mankind in the form of blood or milk ever since. Besides this, artificial systems have gained a significant importance for our daily life during the last decades.

Therefore, it is of special interest to gain an understanding of which interparticle forces govern the stability of colloidal dispersions and how this stability can be tailored. In electrolyte solutions, the classical DLVO theory describes these interactions. Whilst this description provides a good agreement with experimental data for 1:1 electrolytes, larger deviations appear for systems of higher valency. For a detailed examination of the van der Waals and electrostatically dominated regimes, we directly measure the forces between colloidal silica particles in aqueous solutions by the colloidal probe AFM (atomic force microscopy) technique.

Varying the concentration of monovalent salts and acids allows us to demonstrate the transition from the double layer to the van der Waals dominated regime and to determine the pH dependence of the colloidal probes double layer potential. Similar measurements for phosphotungstic (PTA, a 1:3 system) and silicotungstic acid (STA, a 1:4 system) - both nanometer-sized anions of the Keggin type - can still be described with the DLVO theory, but reveal significant deviations between the calculated and measured ionic strengths.