Measuring single-nanoparticle wetting properties by freeze-fracture shadow-casting cryo-scanning electron microscopy

Area of Science:

• Nanotechnology and Materials Science
• Surface Science and Interfacial Phenomena

Background:

• Nanoparticles at fluid interfaces are vital for applications such as drug delivery, biological membrane uptake, emulsion stabilization, and nanocomposite fabrication.
• Understanding nanoscale wetting, particularly the three-phase contact angle (θ), is essential for controlling nanoparticle surface properties but remains a significant challenge for individual nanoparticles.

Purpose of the Study:

• To develop and demonstrate a novel in situ method for measuring the contact angles of individual nanoparticles at fluid interfaces.
• To overcome the limitations of current techniques in characterizing nanoscale wetting phenomena.

Main Methods:

• Utilized freeze-fracture shadow-casting cryo-scanning electron microscopy (cryo-SEM) for in situ contact angle measurement.
• Applied the technique to individual nanoparticles with diameters as small as 10 nm.

Main Results:

• Successfully measured contact angles for individual nanoparticles, significantly advancing the state-of-the-art in nanoscale wetting characterization.
• Demonstrated the method's general applicability across various nanoparticle types, including hydrophilic, hydrophobic, organic, and inorganic materials.
• Observed significant heterogeneity in the wetting behavior of nanoparticles.

Conclusions:

• The developed cryo-SEM method provides unprecedented precision for measuring nanoparticle contact angles.
• This technique is broadly applicable to diverse nanomaterials, facilitating the design of advanced nanoparticle-based systems.
• The observed wetting heterogeneity highlights the complexity of nanoparticle interfacial behavior and the need for precise characterization.