AFM colloidal forces measured between microscopic probes and flat substrates in nanoparticle suspensions.

Area of Science:

• Colloid and Surface Science
• Nanomaterials Characterization
• Atomic Force Microscopy Applications

Background:

• Understanding colloidal forces is crucial for nanoparticle applications.
• Atomic Force Microscopy (AFM) is a key technique for measuring forces at the nanoscale.
• Nanoparticle behavior in confined liquid films influences material properties.

Purpose of the Study:

• To measure colloidal forces between AFM probes and substrates in nanoparticle suspensions.
• To investigate the structural effects of nanoparticles within liquid films.
• To correlate force oscillations with nanoparticle size and surface charge.

Main Methods:

• Utilized AFM with silicon nitride tips and glass sphere probes (5-15 µm).
• Employed mica and silicon wafer substrates in aqueous suspensions of alumina (5-80 nm) and silica (10 nm) nanoparticles.
• Obtained oscillatory force profiles to analyze interactions.

Main Results:

• Observed stratified nanoparticle layers in liquid films between probe and substrate.
• Detected oscillatory structural forces with periodicity related to nanoparticle size.
• Found that oppositely charged nanoparticles coated probes, hindering direct contact.

Conclusions:

• Nanoparticle stratification within liquid films significantly impacts measured colloidal forces.
• Structural forces arise from ordered nanoparticle arrangements, showing periodicity linked to particle dimensions.
• Surface charge plays a critical role in nanoparticle-probe interactions and film formation.