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O: Fachverband Oberflächenphysik

O 69: Poster: Solid-Liquid Interfaces

O 69.13: Poster

Wednesday, March 29, 2023, 18:00–20:00, P2/EG

Correlation between electrostatic and hydration forces on silica and gibbsite surfaces: An Atomic Force Microscopy Study — •Igor Siretanu, Aram Klaassen, and Frieder Mugele — Physics of Complex Fluids Group, MESA+ Institute, Faculty of Science and Technology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands

The balance between hydration and Derjaguin Landau Verwey Overbeek forces at solid-liquid interfaces controls many processes, such as colloidal stability, electrochemistry and ion adsorption. Yet, the hydration forces origin and their relation to the surface charge density controlling the continuum scale electrostatic forces are poorly understood. We argue that these two types of forces are largely independent of each other. Here we performed AFM using intermediate-sized tips that enable the simultaneous detection of DLVO and oscillatory hydration forces at the interface between gibbsite:silica-aqueous electrolyte interfaces. We extract surface charge densities from forces using DLVO theory in combination with a charge regulation boundary conditions for variable pHs and salt concentrations. We simultaneously observe both DLVO and oscillatory hydration forces for an individual crystalline gibbsite particle and the amorphous silica for all fluid compositions. While the diffuse layer charge varies with pH as expected, the oscillatory hydration forces are largely independent of pH and salt concentration, supporting our hypothesis that both forces indeed have a very different origin. We rationalize this based on the distribution of OH groups available for H-bonding on the two distinct surfaces.