Extracting local surface charges and charge regulation behavior from atomic force microscopy measurements at
Cunlu Zhao1, Daniel Ebeling, Igor Siretanu
1Physics of Complex Fluids Group and MESA+ Institute, Faculty of Science and Technology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands. f.mugele@utwente.nl.
Nanoscale
|September 18, 2015
Summary
This study introduces a new Atomic Force Microscopy (AFM) method to measure local surface charge at solid-liquid interfaces, accounting for proton and ion equilibrium shifts. The technique provides consistent results for silica but faces challenges with complex gibbsite nanoparticle surfaces.
Area of Science:
- Surface Science
- Physical Chemistry
- Materials Science
Background:
- Determining local surface charge at solid-liquid interfaces is crucial for understanding interfacial phenomena.
- Traditional methods often overlook the dynamic changes in ion adsorption/desorption equilibria near the interface.
- Atomic Force Microscopy (AFM) offers high spatial resolution for probing these interfaces.
Purpose of the Study:
- To develop and validate a novel AFM-based method for quantifying local surface charge.
- To incorporate charge regulation effects due to proton and ion adsorption/desorption into AFM force measurements.
- To apply the method to heterogeneous silica and gibbsite nanoparticle surfaces in aqueous electrolytes.
Main Methods:
- Recording dynamic mode AFM force-distance curves on silica and gibbsite nanoparticle surfaces.
- Analyzing forces using Derjaguin-Landau-Verwey-Overbeek (DLVO) theory combined with a charge regulation model.
- Developing a simultaneous least-squared fitting approach to extract equilibrium constants from data at varying salt concentrations.
Main Results:
- The developed method successfully determines local surface charge for silica-electrolyte interfaces with high consistency.
- Equilibrium constants for proton and ion reactions at silica surfaces were systematically extracted.
- Surface charge determination for gibbsite nanoparticles was achieved, but specific surface speciation reactions remained ambiguous.
Conclusions:
- The novel AFM method effectively quantifies local surface charge by accounting for dynamic charge regulation.
- The approach provides reliable data for silica surfaces, enabling extraction of reaction equilibrium constants.
- Further investigation is needed to resolve surface speciation complexities on heterogeneous nanomaterials like gibbsite.
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