Interfacial gas nanobubbles or oil nanodroplets?

Area of Science:

• Surface science
• Nanotechnology
• Materials science

Background:

• Nanobubbles are stable gaseous entities at solid-liquid interfaces, extensively studied using Atomic Force Microscopy (AFM).
• Polydimethylsiloxane (PDMS) nanodroplets can be mistaken for nanobubbles in AFM measurements, leading to misinterpretations.
• A reliable method to differentiate nanobubbles from PDMS nanodroplets in situ is urgently needed for accurate AFM analysis.

Purpose of the Study:

• To develop a method for producing polydimethylsiloxane (PDMS) nanodroplets on a highly ordered pyrolytic graphite (HOPG)/water interface.
• To establish a direct experimental approach for distinguishing between nanobubbles and PDMS nanodroplets using AFM.
• To provide a practical solution for accurate nanobubble research by preventing misidentification.

Main Methods:

• Fabrication of PDMS nanodroplets on HOPG/water interfaces using a reproducible method.
• Characterization of nanodroplets and nanobubbles using Atomic Force Microscopy (AFM).
• Analysis of AFM force curves, including approach and retraction phases, to identify distinguishing features.

Main Results:

• PDMS nanodroplets were successfully produced and exhibited similar size, contact angle, and stiffness to nanobubbles.
• A significant difference was observed in AFM force curves: nanobubbles showed a plateau, while PDMS nanodroplets displayed linear force changes.
• This distinct force curve signature allows for reliable in situ discrimination between nanobubbles and PDMS nanodroplets.

Conclusions:

• The study provides an effective method for generating PDMS nanodroplets on HOPG/water interfaces.
• AFM force curve analysis offers a simple, practical, and in situ method to differentiate nanobubbles from PDMS nanodroplets.
• This differentiation is critical for advancing accurate nanobubble research and applications using AFM.