Water and 2-propanol structured on calcite (104) probed by frequency-modulation atomic force microscopy.

Area of Science:

• Surface Science
• Physical Chemistry
• Materials Science

Background:

• Understanding liquid-solid interfaces is crucial in various scientific fields.
• Calcite (CaCO3) surfaces are prevalent in geological and biological systems.
• Previous studies suggested specific density distributions for water and ethanol on calcite.

Purpose of the Study:

• To investigate the interfacial structure of liquid water and 2-propanol on the calcite (104) surface.
• To provide direct experimental evidence of liquid molecule organization at the nanoscale.

Main Methods:

• Frequency-modulation atomic force microscopy (FM-AFM) was employed to probe the liquid-surface interactions.
• The AFM tip scanned the liquids, recording tip-surface forces influenced by interfacial liquid structure.
• Analysis focused on force distributions to infer density modulations.

Main Results:

• Liquid water exhibited a 0.5-nm-thick checkerboard-like force distribution, mirroring the calcite surface topography.
• This pattern indicates lateral and vertical modulation of water density at the interface.
• 2-propanol displayed a laterally uniform, vertically layered structure between the first adsorbed layer and the bulk liquid.

Conclusions:

• The study provides direct AFM evidence of nanoscale liquid structuring at the calcite interface.
• Observed water and 2-propanol structures align with theoretical and simulation-based predictions.
• These findings enhance our understanding of solvation effects on mineral surfaces.