Visualization of hydration layers on muscovite mica in aqueous solution by frequency-modulation atomic force...

Area of Science:

• Surface science
• Physical chemistry
• Nanotechnology

Background:

• Understanding hydration layers at interfaces is crucial for various chemical and physical processes.
• Atomic Force Microscopy (AFM) offers high-resolution imaging capabilities for interfacial phenomena.

Purpose of the Study:

• To visualize and characterize the complex hydration structures on a muscovite mica surface in an aqueous solution.
• To correlate experimental force mapping data with theoretical predictions of water molecule distribution.

Main Methods:

• Utilized a high-resolution, low-thermal drift frequency-modulation atomic force microscope (FM-AFM).
• Collected three-dimensional interaction force mapping data, specifically oscillatory frequency shift versus distance curves.
• Reconstructed two-dimensional frequency shift maps and performed site-specific force versus distance curve analysis.

Main Results:

• Visualized intricate hydration structures on the mica surface, presenting as dot-like or honeycomb-like patterns.
• Observed distinct patterns at different tip-sample distances, with a 0.2 nm separation, aligning with theoretical water molecule density maps.
• Demonstrated good agreement between experimentally obtained site-specific force curves and molecular dynamics simulations.

Conclusions:

• The first hydration layer exhibits a honeycomb-like pattern, while the second layer shows a dot-like pattern in 2D frequency shift images.
• These patterns correspond to the lateral distribution function within each respective hydration layer.
• The study successfully visualizes and quantifies interfacial water structures, validating theoretical models through advanced AFM techniques.